diff --git a/plugins/kolab_delegation/kolab_delegation_engine.php b/plugins/kolab_delegation/kolab_delegation_engine.php
index a286e4b2..48c934b2 100644
--- a/plugins/kolab_delegation/kolab_delegation_engine.php
+++ b/plugins/kolab_delegation/kolab_delegation_engine.php
@@ -1,969 +1,969 @@
 <?php
 
 /**
  * Kolab Delegation Engine
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2011-2012, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_delegation_engine
 {
     public $context;
 
     private $rc;
     private $ldap;
     private $ldap_filter;
     private $ldap_delegate_field;
     private $ldap_login_field;
     private $ldap_name_field;
     private $ldap_email_field;
     private $ldap_org_field;
     private $ldap_dn;
     private $cache = array();
     private $folder_types = array('mail', 'event', 'task');
     private $supported;
 
     const ACL_READ  = 1;
     const ACL_WRITE = 2;
 
     /**
      * Class constructor
      */
     public function __construct()
     {
         $this->rc = rcube::get_instance();
     }
 
     /**
      * Add delegate
      *
      * @param string|array $delegate Delegate DN (encoded) or delegate data (result of delegate_get())
      * @param array        $acl      List of folder->right map
      *
      * @return string On error returns an error label, on success returns null
      */
     public function delegate_add($delegate, $acl)
     {
         if (!is_array($delegate)) {
             $delegate = $this->delegate_get($delegate);
         }
 
         $dn = $delegate['ID'];
         if (empty($delegate) || empty($dn)) {
             return 'createerror';
         }
 
         $list = $this->list_delegates();
         $list = array_keys((array)$list);
         $list = array_filter($list);
 
         if (in_array($dn, $list)) {
             return 'delegationexisterror';
         }
 
         // add delegate to the list
         $list[] = $dn;
         $list   = array_map(array('kolab_ldap', 'dn_decode'), $list);
 
         // update user record
         $result = $this->user_update_delegates($list);
 
         // Set ACL on folders
         if ($result && !empty($acl)) {
             $this->delegate_acl_update($delegate['uid'], $acl);
         }
 
         return $result ? null : 'createerror';
     }
 
     /**
      * Set/Update ACL on delegator's folders
      *
      * @param string $uid    Delegate authentication identifier
      * @param array  $acl    List of folder->right map
      * @param bool   $update Update (remove) old rights
      *
      * @return string On error returns an error label, on success returns null
      */
     public function delegate_acl_update($uid, $acl, $update = false)
     {
         $storage     = $this->rc->get_storage();
         $right_types = $this->right_types();
         $folders     = $update ? $this->list_folders($uid) : array();
 
         foreach ($acl as $folder_name => $rights) {
-            $r = $right_types[$rights];
+            $r = $right_types[$rights] ?? null;
             if ($r) {
                 $storage->set_acl($folder_name, $uid, $r);
             }
             else {
                 $storage->delete_acl($folder_name, $uid);
             }
 
             if (!empty($folders) && isset($folders[$folder_name])) {
                 unset($folders[$folder_name]);
             }
         }
 
         foreach ($folders as $folder_name => $folder) {
-            if ($folder['rights']) {
+            if (!empty($folder['rights'])) {
                 $storage->delete_acl($folder_name, $uid);
             }
         }
     }
 
     /**
      * Delete delgate
      *
      * @param string $dn      Delegate DN (encoded)
      * @param bool   $acl_del Enable ACL deletion on delegator folders
      *
      * @return string On error returns an error label, on success returns null
      */
     public function delegate_delete($dn, $acl_del = false)
     {
         $delegate = $this->delegate_get($dn);
         $list     = $this->list_delegates();
         $user     = $this->user();
 
         if (empty($delegate) || !isset($list[$dn])) {
             return 'deleteerror';
         }
 
         // remove delegate from the list
         unset($list[$dn]);
         $list = array_keys($list);
         $list = array_map(array('kolab_ldap', 'dn_decode'), $list);
         $user[$this->ldap_delegate_field] = $list;
 
         // update user record
         $result = $this->user_update_delegates($list);
 
         // remove ACL
         if ($result && $acl_del) {
             $this->delegate_acl_update($delegate['uid'], array(), true);
         }
 
         return $result ? null : 'deleteerror';
     }
 
     /**
      * Return delegate data
      *
      * @param string $dn Delegate DN (encoded)
      *
      * @return array Delegate record (ID, name, uid, imap_uid)
      */
     public function delegate_get($dn)
     {
         // use internal cache so we not query LDAP more than once per request
         if (!isset($this->cache[$dn])) {
             $ldap = $this->ldap();
 
             if (!$ldap || empty($dn)) {
                 return array();
             }
 
             // Get delegate
             $user = $ldap->get_record(kolab_ldap::dn_decode($dn));
 
             if (empty($user)) {
                 return array();
             }
 
             $delegate = $this->parse_ldap_record($user);
             $delegate['ID'] = $dn;
 
             $this->cache[$dn] = $delegate;
         }
 
         return $this->cache[$dn];
     }
 
     /**
      * Return delegate data
      *
      * @param string $login Delegate name (the 'uid' returned in get_users())
      *
      * @return array Delegate record (ID, name, uid, imap_uid)
      */
     public function delegate_get_by_name($login)
     {
         $ldap = $this->ldap();
 
         if (!$ldap || empty($login)) {
             return array();
         }
 
         $list = $ldap->dosearch($this->ldap_login_field, $login, 1);
 
         if (count($list) == 1) {
             $dn   = key($list);
             $user = $list[$dn];
 
             return $this->parse_ldap_record($user, $dn);
         }
     }
 
     /**
      * LDAP object getter
      */
     private function ldap()
     {
         if ($this->ldap !== null) {
             return $this->ldap;
         }
 
         $this->ldap = kolab_storage::ldap('kolab_delegation_addressbook');
 
         if (!$this->ldap || !$this->ldap->ready) {
             return null;
         }
 
         // Default filter of LDAP queries
         $this->ldap_filter = $this->rc->config->get('kolab_delegation_filter', '(|(objectClass=kolabInetOrgPerson)(&(objectclass=kolabsharedfolder)(kolabFolderType=mail)))');
         // Name of the LDAP field for delegates list
         $this->ldap_delegate_field = $this->rc->config->get('kolab_delegation_delegate_field', 'kolabDelegate');
         // Encoded LDAP DN of current user, set on login by kolab_auth plugin
         $this->ldap_dn = $_SESSION['kolab_dn'];
 
         // Name of the LDAP field with authentication ID
         $this->ldap_login_field = $this->rc->config->get('kolab_delegation_login_field', $this->rc->config->get('kolab_auth_login'));
         // Name of the LDAP field with user name used for identities
         $this->ldap_name_field = $this->rc->config->get('kolab_delegation_name_field', $this->rc->config->get('kolab_auth_name'));
         // Name of the LDAP field with email addresses used for identities
         $this->ldap_email_field = $this->rc->config->get('kolab_delegation_email_field', $this->rc->config->get('kolab_auth_email'));
         // Name of the LDAP field with organization name for identities
         $this->ldap_org_field = $this->rc->config->get('kolab_delegation_organization_field', $this->rc->config->get('kolab_auth_organization'));
 
         $this->ldap->set_filter($this->ldap_filter);
         $this->ldap->extend_fieldmap(array($this->ldap_delegate_field => $this->ldap_delegate_field));
 
         return $this->ldap;
     }
 
     /**
      * List current user delegates
      */
     public function list_delegates()
     {
         $result = array();
         $ldap   = $this->ldap();
         $user   = $this->user();
 
         if (empty($ldap) || empty($user)) {
             return array();
         }
 
         // Get delegates of current user
         $delegates = $user[$this->ldap_delegate_field] ?? null;
 
         if (!empty($delegates)) {
             foreach ((array)$delegates as $dn) {
                 $delegate = $ldap->get_record($dn);
                 $data     = $this->parse_ldap_record($delegate, $dn);
 
                 if (!empty($data) && !empty($data['name'])) {
                     $result[$data['ID']] = $data['name'];
                 }
             }
         }
 
         return $result;
     }
 
     /**
      * List current user delegators
      *
      * @return array List of delegators
      */
     public function list_delegators()
     {
         $result = array();
         $ldap   = $this->ldap();
 
         if (empty($ldap) || empty($this->ldap_dn)) {
             return array();
         }
 
         $list = $ldap->dosearch($this->ldap_delegate_field, $this->ldap_dn, 1);
 
         foreach ($list as $dn => $delegator) {
             $delegator = $this->parse_ldap_record($delegator, $dn);
             $result[$delegator['ID']] = $delegator;
         }
 
         return $result;
     }
 
     /**
      * List current user delegators in format compatible with Calendar plugin
      *
      * @return array List of delegators
      */
     public function list_delegators_js()
     {
         $list   = $this->list_delegators();
         $result = array();
 
         foreach ($list as $delegator) {
             $name = $delegator['name'];
             if ($pos = strrpos($name, '(')) {
                 $name = trim(substr($name, 0, $pos));
             }
 
             $result[$delegator['imap_uid']] = array(
                 'emails' => ';' . implode(';', $delegator['email']),
                 'email'  => $delegator['email'][0],
                 'name'   => $name,
             );
         }
 
         return $result;
     }
 
     /**
      * Prepare namespace prefixes for JS environment
      *
      * @return array List of prefixes
      */
     public function namespace_js()
     {
         $storage = $this->rc->get_storage();
         $ns      = $storage->get_namespace('other');
 
         if ($ns) {
             foreach ($ns as $idx => $nsval) {
                 $ns[$idx] = kolab_storage::folder_id($nsval[0]);
             }
         }
 
         return $ns;
     }
 
     /**
      * Get all folders to which current user has admin access
      *
      * @param string $delegate IMAP user identifier
      *
      * @return array Folder type/rights
      */
     public function list_folders($delegate = null)
     {
         $storage  = $this->rc->get_storage();
         $folders  = $storage->list_folders();
         $metadata = kolab_storage::folders_typedata();
         $result   = array();
 
         if (!is_array($metadata)) {
             return $result;
         }
 
         // Definition of read and write ACL
         $right_types = $this->right_types();
 
         $delegate_lc = strtolower((string) $delegate);
 
         foreach ($folders as $folder) {
             // get only folders in personal namespace
             if ($storage->folder_namespace($folder) != 'personal') {
                 continue;
             }
 
             $rights = null;
             $type   = !empty($metadata[$folder]) ? $metadata[$folder] : 'mail';
             list($class, $subclass) = strpos($type, '.') ? explode('.', $type) : [$type, ''];
 
             if (!in_array($class, $this->folder_types)) {
                 continue;
             }
 
             // in edit mode, get folder ACL
             if ($delegate) {
                 // @TODO: cache ACL
                 $imap_acl = $storage->get_acl($folder);
                 if (!empty($imap_acl) && (($acl = ($imap_acl[$delegate] ?? null)) || ($acl = ($imap_acl[$delegate_lc] ?? null)))) {
                     if ($this->acl_compare($acl, $right_types[self::ACL_WRITE])) {
                         $rights = self::ACL_WRITE;
                     }
                     else if ($this->acl_compare($acl, $right_types[self::ACL_READ])) {
                         $rights = self::ACL_READ;
                     }
                 }
             }
             else if ($folder == 'INBOX' || $subclass == 'default' || $subclass == 'inbox') {
                 $rights = self::ACL_WRITE;
             }
 
             $result[$folder] = array(
                 'type'   => $class,
                 'rights' => $rights,
             );
         }
 
         return $result;
     }
 
     /**
      * Returns list of users for autocompletion
      *
      * @param string $search Search string
      *
      * @return array Users list
      */
     public function list_users($search)
     {
         $ldap = $this->ldap();
 
         if (empty($ldap) || $search === '' || $search === null) {
             return array();
         }
 
         $max    = (int) $this->rc->config->get('autocomplete_max', 15);
         $mode   = (int) $this->rc->config->get('addressbook_search_mode');
         $fields = array_unique(array_filter(array_merge((array)$this->ldap_name_field, (array)$this->ldap_login_field)));
         $users  = array();
         $keys   = array();
 
         $result = $ldap->dosearch($fields, $search, $mode, (array)$this->ldap_login_field, $max);
 
         foreach ($result as $record) {
             // skip self
             if ($record['dn'] == $_SESSION['kolab_dn']) {
                 continue;
             }
 
             $user = $this->parse_ldap_record($record);
 
             if ($user['uid']) {
                 $display = rcube_addressbook::compose_search_name($record);
                 $user    = array('name' => $user['uid'], 'display' => $display);
                 $users[] = $user;
                 $keys[]  = $display ?: $user['uid'];
             }
         }
 
         if (count($users)) {
             // sort users index
             asort($keys, SORT_LOCALE_STRING);
             // re-sort users according to index
             foreach (array_keys($keys) as $idx) {
                 $keys[$idx] = $users[$idx];
             }
             $users = array_values($keys);
         }
 
         return $users;
     }
 
     /**
      * Extract delegate identifiers and pretty name from LDAP record
      */
     private function parse_ldap_record($data, $dn = null)
     {
         $email = array();
         $uid   = $data[$this->ldap_login_field];
 
         if (is_array($uid)) {
             $uid = array_filter($uid);
             $uid = $uid[0];
         }
 
         // User name for identity
         foreach ((array)$this->ldap_name_field as $field) {
             $name = is_array($data[$field]) ? $data[$field][0] : $data[$field];
             if (!empty($name)) {
                 break;
             }
         }
 
         // User email(s) for identity
         foreach ((array)$this->ldap_email_field as $field) {
             $user_email = is_array($data[$field]) ? array_filter($data[$field]) : $data[$field];
             if (!empty($user_email)) {
                 $email = array_merge((array)$email, (array)$user_email);
             }
         }
 
         // Organization for identity
         foreach ((array)$this->ldap_org_field as $field) {
             $organization = is_array($data[$field]) ? $data[$field][0] : $data[$field];
             if (!empty($organization)) {
                 break;
             }
         }
 
         $realname = $name;
         if ($uid && $name) {
             $name .= ' (' . $uid . ')';
         }
         else {
             $name = $uid;
         }
 
         // get IMAP uid - identifier used in shared folder hierarchy
         $imap_uid = $uid;
         if ($pos = strpos($imap_uid, '@')) {
             $imap_uid = substr($imap_uid, 0, $pos);
         }
 
         return array(
             'ID'       => kolab_ldap::dn_encode($dn),
             'uid'      => $uid,
             'name'     => $name,
             'realname' => $realname,
             'imap_uid' => $imap_uid,
             'email'    => $email,
             'organization' => $organization ?? null,
         );
     }
 
     /**
      * Returns LDAP record of current user
      *
      * @return array User data
      */
     public function user($parsed = false)
     {
         if (!isset($this->cache['user'])) {
             $ldap = $this->ldap();
 
             if (!$ldap) {
                 return array();
             }
 
             // Get current user record
             $this->cache['user'] = $ldap->get_record($this->ldap_dn);
         }
 
         return $parsed ? $this->parse_ldap_record($this->cache['user']) : $this->cache['user'];
     }
 
     /**
      * Update LDAP record of current user
      *
      * @param array List of delegates
      */
     public function user_update_delegates($list)
     {
         $ldap = $this->ldap();
         $pass = $this->rc->decrypt($_SESSION['password']);
 
         if (!$ldap) {
             return false;
         }
 
         // need to bind as self for sufficient privilages
         if (!$ldap->bind($this->ldap_dn, $pass)) {
             return false;
         }
 
         $user[$this->ldap_delegate_field] = $list;
 
         unset($this->cache['user']);
 
         // replace delegators list in user record
         return $ldap->replace($this->ldap_dn, $user);
     }
 
     /**
      * Manage delegation data on user login
      */
     public function delegation_init()
     {
         // Fetch all delegators from LDAP who assigned the
         // current user as their delegate and create identities
         //  a) if identity with delegator's email exists, continue
         //  b) create identity ($delegate on behalf of $delegator
         //        <$delegator-email>) for new delegators
         //  c) remove all other identities which do not match the user's primary
         //       or alias email if 'kolab_delegation_purge_identities' is set.
 
         $delegators = $this->list_delegators();
         $use_subs   = $this->rc->config->get('kolab_use_subscriptions');
         $identities = $this->rc->user->list_emails();
         $emails     = array();
         $uids       = array();
 
         if (!empty($delegators)) {
             $storage  = $this->rc->get_storage();
             $other_ns = $storage->get_namespace('other') ?: array();
             $folders  = $storage->list_folders();
         }
 
         // convert identities to simpler format for faster access
         foreach ($identities as $idx => $ident) {
             // get user name from default identity
             if (!$idx) {
                 $default = array(
                     'name' => $ident['name'],
                 );
             }
             $emails[$ident['identity_id']] = $ident['email'];
         }
 
         // for every delegator...
         foreach ($delegators as $delegator) {
             $uids[$delegator['imap_uid']] = $email_arr = $delegator['email'];
             $diff = array_intersect($emails, $email_arr);
 
             // identity with delegator's email already exist, do nothing
             if (count($diff)) {
                 $emails = array_diff($emails, $email_arr);
                 continue;
             }
 
             // create identities for delegator emails
             foreach ($email_arr as $email) {
                 // @TODO: "Delegatorname" or "Username on behalf of Delegatorname"?
                 $default['name']  = $delegator['realname'];
                 $default['email'] = $email;
                 // Database field for organization is NOT NULL
                 $default['organization'] = empty($delegator['organization']) ? '' : $delegator['organization'];
                 $this->rc->user->insert_identity($default);
             }
 
             // IMAP folders shared by new delegators shall be subscribed on login,
             // as well as existing subscriptions of previously shared folders shall
             // be removed. I suppose the latter one is already done in Roundcube.
 
             // for every accessible folder...
             foreach ($folders as $folder) {
                 // for every 'other' namespace root...
                 foreach ($other_ns as $ns) {
                     $prefix = $ns[0] . $delegator['imap_uid'];
                     // subscribe delegator's folder
                     if ($folder === $prefix || strpos($folder, $prefix . substr($ns[0], -1)) === 0) {
                         // Event/Task folders need client-side activation
                         $type = kolab_storage::folder_type($folder);
                         if (preg_match('/^(event|task)/i', $type)) {
                             kolab_storage::folder_activate($folder);
                         }
                         // Subscribe to mail folders and (if system is configured
                         // to display only subscribed folders) to other
                         if ($use_subs || preg_match('/^mail/i', $type)) {
                             $storage->subscribe($folder);
                         }
                     }
                 }
             }
         }
 
         // remove identities that "do not belong" to user nor delegators
         if ($this->rc->config->get('kolab_delegation_purge_identities')) {
             $user   = $this->user(true);
             $emails = array_diff($emails, $user['email']);
 
             foreach (array_keys($emails) as $idx) {
                 $this->rc->user->delete_identity($idx);
             }
         }
 
         $_SESSION['delegators'] = $uids;
     }
 
     /**
      * Sets delegator context according to email message recipient
      *
      * @param rcube_message $message Email message object
      */
     public function delegator_context_from_message($message)
     {
         if (empty($_SESSION['delegators'])) {
             return;
         }
 
         // Match delegators' addresses with message To: address
         // @TODO: Is this reliable enough?
         // Roundcube sends invitations to every attendee separately,
         // but maybe there's a software which sends with CC header or many addresses in To:
 
         $emails = $message->get_header('to');
         $emails = rcube_mime::decode_address_list($emails, null, false);
 
         foreach ($emails as $email) {
             foreach ($_SESSION['delegators'] as $uid => $addresses) {
                 if (in_array($email['mailto'], $addresses)) {
                     return $this->context = $uid;
                 }
             }
         }
     }
 
     /**
      * Return (set) current delegator context
      *
      * @return string Delegator UID
      */
     public function delegator_context()
     {
         if (!$this->context && !empty($_SESSION['delegators'])) {
             $context = rcube_utils::get_input_value('_context', rcube_utils::INPUT_GPC);
             if ($context && isset($_SESSION['delegators'][$context])) {
                 $this->context = $context;
             }
         }
 
         return $this->context;
     }
 
     /**
      * Set user identity according to delegator delegator
      *
      * @param array $args Reference to plugin hook arguments
      */
     public function delegator_identity_filter(&$args)
     {
         $context = $this->delegator_context();
 
         if (!$context) {
             return;
         }
 
         $identities = $this->rc->user->list_emails();
         $emails     = $_SESSION['delegators'][$context];
 
         foreach ($identities as $ident) {
             if (in_array($ident['email'], $emails)) {
                 $args['identity'] = $ident;
                 return;
             }
         }
 
         // fallback to default identity
         $args['identity'] = array_shift($identities);
     }
 
     /**
      * Filter user emails according to delegator context
      *
      * @param array $args Reference to plugin hook arguments
      */
     public function delegator_emails_filter(&$args)
     {
         $context = $this->delegator_context();
 
         // try to derive context from the given user email
         if (!$context && !empty($args['emails'])) {
             if (($user = preg_replace('/@.+$/', '', $args['emails'][0])) && isset($_SESSION['delegators'][$user])) {
                 $context = $user;
             }
         }
 
         // return delegator's addresses
         if ($context) {
             $args['emails'] = $_SESSION['delegators'][$context];
             $args['abort']  = true;
         }
         // return only user addresses (exclude all delegators addresses)
         else if (!empty($_SESSION['delegators'])) {
             $identities = $this->rc->user->list_emails();
             $emails[]   = $this->rc->user->get_username();
 
             foreach ($identities as $identity) {
                 $emails[] = $identity['email'];
             }
 
             foreach ($_SESSION['delegators'] as $delegator_emails) {
                 $emails = array_diff($emails, $delegator_emails);
             }
 
             $args['emails'] = array_unique($emails);
             $args['abort']  = true;
         }
     }
 
     /**
      * Filters list of calendar/task folders according to delegator context
      *
      * @param array $args Reference to plugin hook arguments
      */
     public function delegator_folder_filter(&$args, $mode = 'calendars')
     {
         $context = $this->delegator_context();
 
         if (empty($context)) {
             return $args;
         }
 
         $storage  = $this->rc->get_storage();
         $other_ns = $storage->get_namespace('other') ?: array();
         $delim    = $storage->get_hierarchy_delimiter();
 
         if ($mode == 'calendars') {
             $editable = $args['filter'] & calendar_driver::FILTER_WRITEABLE;
             $active   = $args['filter'] & calendar_driver::FILTER_ACTIVE;
             $personal = $args['filter'] & calendar_driver::FILTER_PERSONAL;
             $shared   = $args['filter'] & calendar_driver::FILTER_SHARED;
         }
         else {
             $editable = $args['filter'] & tasklist_driver::FILTER_WRITEABLE;
             $active   = $args['filter'] & tasklist_driver::FILTER_ACTIVE;
             $personal = $args['filter'] & tasklist_driver::FILTER_PERSONAL;
             $shared   = $args['filter'] & tasklist_driver::FILTER_SHARED;
         }
 
         $folders = array();
 
         foreach ($args['list'] as $folder) {
             if (isset($folder->ready) && !$folder->ready) {
                 continue;
             }
 
             if ($editable && !$folder->editable) {
                 continue;
             }
 
             if ($active && !$folder->storage->is_active()) {
                 continue;
             }
 
             if ($personal || $shared) {
                 $ns = $folder->get_namespace();
 
                 if ($personal && $ns == 'personal') {
                     continue;
                 }
                 else if ($personal && $ns == 'other') {
                     $found = false;
                     foreach ($other_ns as $ns) {
                         $c_folder = $ns[0] . $context . $delim;
                         if (strpos($folder->name, $c_folder) === 0) {
                             $found = true;
                         }
                     }
 
                     if (!$found) {
                         continue;
                     }
                 }
                 else if (!$shared || $ns != 'shared') {
                     continue;
                 }
             }
 
             $folders[$folder->id] = $folder;
         }
 
         $args[$mode]   = $folders;
         $args['abort'] = true;
     }
 
     /**
      * Filters/updates message headers according to delegator context
      *
      * @param array $args Reference to plugin hook arguments
      */
     public function delegator_delivery_filter(&$args)
     {
         // no context, but message still can be send on behalf of...
         if (!empty($_SESSION['delegators'])) {
             $message = $args['message'];
             $headers = $message->headers();
 
             // get email address from From: header
             $from = rcube_mime::decode_address_list($headers['From']);
             $from = array_shift($from);
             $from = $from['mailto'];
 
             foreach ($_SESSION['delegators'] as $uid => $addresses) {
                 if (in_array($from, $addresses)) {
                     $context = $uid;
                     break;
                 }
             }
 
             // add Sender: header with current user default identity
             if (!empty($context)) {
                 $identity = $this->rc->user->get_identity();
                 $sender   = format_email_recipient($identity['email'], $identity['name']);
 
                 $message->headers(array('Sender' => $sender), false, true);
             }
         }
     }
 
     /**
      * Compares two ACLs (according to supported rights)
      *
      * @param array $acl1 ACL rights array (or string)
      * @param array $acl2 ACL rights array (or string)
      *
      * @param bool True if $acl1 contains all rights from $acl2
      */
     function acl_compare($acl1, $acl2)
     {
         if (!is_array($acl1)) $acl1 = str_split($acl1);
         if (!is_array($acl2)) $acl2 = str_split($acl2);
 
         $rights = $this->rights_supported();
 
         $acl1 = array_intersect($acl1, $rights);
         $acl2 = array_intersect($acl2, $rights);
         $res  = array_intersect($acl1, $acl2);
 
         $cnt1 = count($res);
         $cnt2 = count($acl2);
 
         if ($cnt1 >= $cnt2) {
             return true;
         }
     }
 
     /**
      * Get list of supported access rights (according to RIGHTS capability)
      *
      * @todo: this is stolen from acl plugin, move to rcube_storage/rcube_imap
      *
      * @return array List of supported access rights abbreviations
      */
     public function rights_supported()
     {
         if ($this->supported !== null) {
             return $this->supported;
         }
 
         $storage = $this->rc->get_storage();
         $capa    = $storage->get_capability('RIGHTS');
 
         if (is_array($capa)) {
             $rights = strtolower($capa[0]);
         }
         else {
             $rights = 'cd';
         }
 
         return $this->supported = str_split('lrswi' . $rights . 'pa');
     }
 
     private function right_types()
     {
         // Get supported rights and build column names
         $supported = $this->rights_supported();
 
         // depending on server capability either use 'te' or 'd' for deleting msgs
         $deleteright = implode(array_intersect(str_split('ted'), $supported));
 
         return array(
             self::ACL_READ  => 'lrs',
             self::ACL_WRITE => 'lrswi'.$deleteright,
         );
     }
 }
diff --git a/plugins/kolab_folders/kolab_folders.php b/plugins/kolab_folders/kolab_folders.php
index a6f7fb0f..340901fe 100644
--- a/plugins/kolab_folders/kolab_folders.php
+++ b/plugins/kolab_folders/kolab_folders.php
@@ -1,858 +1,858 @@
 <?php
 
 /**
  * Type-aware folder management/listing for Kolab
  *
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2011-2017, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_folders extends rcube_plugin
 {
     public $task = '?(?!login).*';
 
     public $types      = array('mail', 'event', 'journal', 'task', 'note', 'contact', 'configuration', 'file', 'freebusy');
     public $subtypes   = array(
         'mail'          => array('inbox', 'drafts', 'sentitems', 'outbox', 'wastebasket', 'junkemail'),
         'event'         => array('default'),
         'task'          => array('default'),
         'journal'       => array('default'),
         'note'          => array('default'),
         'contact'       => array('default'),
         'configuration' => array('default'),
         'file'          => array('default'),
         'freebusy'      => array('default'),
     );
     public $act_types  = array('event', 'task');
 
     private $rc;
     private static $instance;
     private $expire_annotation = '/shared/vendor/cmu/cyrus-imapd/expire';
     private $is_processing = false;
 
 
     /**
      * Plugin initialization.
      */
     function init()
     {
         self::$instance = $this;
         $this->rc = rcube::get_instance();
 
         // load required plugin
         $this->require_plugin('libkolab');
 
         // Folder listing hooks
         $this->add_hook('storage_folders', array($this, 'mailboxes_list'));
 
         // Folder manager hooks
         $this->add_hook('folder_form', array($this, 'folder_form'));
         $this->add_hook('folder_update', array($this, 'folder_save'));
         $this->add_hook('folder_create', array($this, 'folder_save'));
         $this->add_hook('folder_delete', array($this, 'folder_save'));
         $this->add_hook('folder_rename', array($this, 'folder_save'));
         $this->add_hook('folders_list', array($this, 'folders_list'));
 
         // Special folders setting
         $this->add_hook('preferences_save', array($this, 'prefs_save'));
 
         // ACL plugin hooks
         $this->add_hook('acl_rights_simple', array($this, 'acl_rights_simple'));
         $this->add_hook('acl_rights_supported', array($this, 'acl_rights_supported'));
 
         // Resolving other user folder names
         $this->add_hook('render_mailboxlist', array($this, 'render_folderlist'));
         $this->add_hook('render_folder_selector', array($this, 'render_folderlist'));
         $this->add_hook('folders_list', array($this, 'render_folderlist'));
     }
 
     /**
      * Handler for mailboxes_list hook. Enables type-aware lists filtering.
      */
     function mailboxes_list($args)
     {
         // infinite loop prevention
         if ($this->is_processing) {
             return $args;
         }
 
         if (!$this->metadata_support()) {
             return $args;
         }
 
         $this->is_processing = true;
 
         // get folders
         $folders = kolab_storage::list_folders($args['root'], $args['name'], $args['filter'], $args['mode'] == 'LSUB', $folderdata);
 
         $this->is_processing = false;
 
         if (!is_array($folders)) {
             return $args;
         }
 
         // Create default folders
         if ($args['root'] == '' && $args['name'] = '*') {
             $this->create_default_folders($folders, $args['filter'], $folderdata, $args['mode'] == 'LSUB');
         }
 
         $args['folders'] = $folders;
 
         return $args;
     }
 
     /**
      * Handler for folders_list hook. Add css classes to folder rows.
      */
     function folders_list($args)
     {
         if (!$this->metadata_support()) {
             return $args;
         }
 
         // load translations
         $this->add_texts('localization/', false);
 
         // Add javascript script to the client
         $this->include_script('kolab_folders.js');
 
         $this->add_label('folderctype');
         foreach ($this->types as $type) {
             $this->add_label('foldertype' . $type);
         }
 
         $skip_namespace = $this->rc->config->get('kolab_skip_namespace');
         $skip_roots     = array();
 
         if (!empty($skip_namespace)) {
             $storage = $this->rc->get_storage();
             foreach ((array)$skip_namespace as $ns) {
                 foreach((array)$storage->get_namespace($ns) as $root) {
                     $skip_roots[] = rtrim($root[0], $root[1]);
                 }
             }
         }
 
         $this->rc->output->set_env('skip_roots', $skip_roots);
         $this->rc->output->set_env('foldertypes', $this->types);
 
         // get folders types
         $folderdata = kolab_storage::folders_typedata();
 
         if (!is_array($folderdata)) {
             return $args;
         }
 
         // Add type-based style for table rows
         // See kolab_folders::folder_class_name()
         if (!empty($args['table'])) {
             $table = $args['table'];
 
             for ($i=1, $cnt=$table->size(); $i<=$cnt; $i++) {
                 $attrib = $table->get_row_attribs($i);
                 $folder = $attrib['foldername']; // UTF7-IMAP
                 $type   = $folderdata[$folder];
 
                 if (!$type) {
                     $type = 'mail';
                 }
 
                 $class_name = self::folder_class_name($type);
                 $attrib['class'] = trim($attrib['class'] . ' ' . $class_name);
                 $table->set_row_attribs($attrib, $i);
             }
         }
 
         // Add type-based class for list items
         if (!empty($args['list']) && is_array($args['list'])) {
             foreach ($args['list'] as $k => $item) {
                 $folder = $item['folder_imap']; // UTF7-IMAP
                 $type   = $folderdata[$folder] ?? null;
 
                 if (!$type) {
                     $type = 'mail';
                 }
 
                 $class_name = self::folder_class_name($type);
                 $args['list'][$k]['class'] = trim($item['class'] . ' ' . $class_name);
             }
         }
 
         return $args;
     }
 
     /**
      * Handler for folder info/edit form (folder_form hook).
      * Adds folder type selector.
      */
     function folder_form($args)
     {
         if (!$this->metadata_support()) {
             return $args;
         }
         // load translations
         $this->add_texts('localization/', false);
 
         // INBOX folder is of type mail.inbox and this cannot be changed
         if ($args['name'] == 'INBOX') {
             $args['form']['props']['fieldsets']['settings']['content']['foldertype'] = array(
                 'label' => $this->gettext('folderctype'),
                 'value' => sprintf('%s (%s)', $this->gettext('foldertypemail'), $this->gettext('inbox')),
             );
 
             $this->add_expire_input($args['form'], 'INBOX');
 
             return $args;
         }
 
         if (!empty($args['options']['is_root'])) {
             return $args;
         }
 
         $mbox = strlen($args['name']) ? $args['name'] : $args['parent_name'];
 
         if (isset($_POST['_ctype'])) {
             $new_ctype   = trim(rcube_utils::get_input_value('_ctype', rcube_utils::INPUT_POST));
             $new_subtype = trim(rcube_utils::get_input_value('_subtype', rcube_utils::INPUT_POST));
         }
 
         // Get type of the folder or the parent
         $subtype = '';
         if (strlen($mbox)) {
             list($ctype, $subtype) = $this->get_folder_type($mbox);
-            if (strlen($args['parent_name']) && $subtype == 'default') {
+            if (isset($args['parent_name']) && strlen($args['parent_name']) && $subtype == 'default') {
                 $subtype = ''; // there can be only one
             }
         }
 
         if (empty($ctype)) {
             $ctype = 'mail';
         }
 
         $storage = $this->rc->get_storage();
 
         // Don't allow changing type of shared folder, according to ACL
         if (strlen($mbox)) {
             $options = $storage->folder_info($mbox);
             if ($options['namespace'] != 'personal' && !in_array('a', (array)$options['rights'])) {
                 if (in_array($ctype, $this->types)) {
                     $value = $this->gettext('foldertype'.$ctype);
                 }
                 else {
                     $value = $ctype;
                 }
                 if ($subtype) {
                     $value .= ' ('. ($subtype == 'default' ? $this->gettext('default') : $subtype) .')';
                 }
 
                 $args['form']['props']['fieldsets']['settings']['content']['foldertype'] = array(
                     'label' => $this->gettext('folderctype'),
                     'value' => $value,
                 );
 
                 return $args;
             }
         }
 
         // Add javascript script to the client
         $this->include_script('kolab_folders.js');
 
         // build type SELECT fields
         $type_select = new html_select(array('name' => '_ctype', 'id' => '_folderctype',
             'onchange' => "\$('[name=\"_expire\"]').attr('disabled', \$(this).val() != 'mail')"
         ));
         $sub_select  = new html_select(array('name' => '_subtype', 'id' => '_subtype'));
         $sub_select->add('', '');
 
         foreach ($this->types as $type) {
             $type_select->add($this->gettext('foldertype'.$type), $type);
         }
         // add non-supported type
         if (!in_array($ctype, $this->types)) {
             $type_select->add($ctype, $ctype);
         }
 
         $sub_types = array();
         foreach ($this->subtypes as $ftype => $subtypes) {
             $sub_types[$ftype] = array_combine($subtypes, array_map(array($this, 'gettext'), $subtypes));
 
             // fill options for the current folder type
             if ($ftype == $ctype || (isset($new_ctype) && $ftype == $new_ctype)) {
                 $sub_select->add(array_values($sub_types[$ftype]), $subtypes);
             }
         }
 
         $args['form']['props']['fieldsets']['settings']['content']['folderctype'] = array(
             'label' => $this->gettext('folderctype'),
             'value' => html::div('input-group',
                 $type_select->show($new_ctype ?? $ctype)
                 . $sub_select->show($new_subtype ?? $subtype)
             ),
         );
 
         $this->rc->output->set_env('kolab_folder_subtypes', $sub_types);
         $this->rc->output->set_env('kolab_folder_subtype', $new_subtype ?? $subtype);
 
         $this->add_expire_input($args['form'], $args['name'], $ctype);
 
         return $args;
     }
 
     /**
      * Handler for folder update/create action (folder_update/folder_create hook).
      */
     function folder_save($args)
     {
         // Folder actions from folders list
         if (empty($args['record'])) {
             return $args;
         }
 
         // Folder create/update with form
         $ctype     = trim(rcube_utils::get_input_value('_ctype', rcube_utils::INPUT_POST));
         $subtype   = trim(rcube_utils::get_input_value('_subtype', rcube_utils::INPUT_POST));
         $mbox      = $args['record']['name'];
         $old_mbox  = $args['record']['oldname'] ?? null;
         $subscribe = $args['record']['subscribe'] ?? true;
 
         if (empty($ctype)) {
             return $args;
         }
 
         // load translations
         $this->add_texts('localization/', false);
 
         // Skip folder creation/rename in core
         // @TODO: Maybe we should provide folder_create_after and folder_update_after hooks?
         //        Using create_mailbox/rename_mailbox here looks bad
         $args['abort']  = true;
 
         // There can be only one default folder of specified type
         if ($subtype == 'default') {
             $default = $this->get_default_folder($ctype);
 
             if ($default !== null && $old_mbox != $default) {
                 $args['result'] = false;
                 $args['message'] = $this->gettext('defaultfolderexists');
                 return $args;
             }
         }
         // Subtype sanity-checks
         else if ($subtype && (!($subtypes = $this->subtypes[$ctype]) || !in_array($subtype, $subtypes))) {
             $subtype = '';
         }
 
         $ctype .= $subtype ? '.'.$subtype : '';
 
         $storage = $this->rc->get_storage();
 
         // Create folder
         if (!strlen($old_mbox)) {
             $result = $storage->create_folder($mbox, $subscribe);
 
             // Set folder type
             if ($result) {
                 $this->set_folder_type($mbox, $ctype);
             }
         }
         // Rename folder
         else {
             if ($old_mbox != $mbox) {
                 $result = $storage->rename_folder($old_mbox, $mbox);
             }
             else {
                 $result = true;
             }
 
             if ($result) {
                 list($oldtype, $oldsubtype) = $this->get_folder_type($mbox);
                 $oldtype .= $oldsubtype ? '.'.$oldsubtype : '';
 
                 if ($ctype != $oldtype) {
                     $this->set_folder_type($mbox, $ctype);
                 }
             }
         }
 
         // Set messages expiration in days
         if ($result && isset($_POST['_expire'])) {
             $expire = trim(rcube_utils::get_input_value('_expire', rcube_utils::INPUT_POST));
             $expire = intval($expire) && preg_match('/^mail/', $ctype) ? intval($expire) : null;
 
             $storage->set_metadata($mbox, array($this->expire_annotation => $expire));
         }
 
         $args['record']['class']     = self::folder_class_name($ctype);
         $args['record']['subscribe'] = $subscribe;
         $args['result'] = $result;
 
         return $args;
     }
 
     /**
      * Handler for user preferences save (preferences_save hook)
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function prefs_save($args)
     {
         if ($args['section'] != 'folders') {
             return $args;
         }
 
         $dont_override = (array) $this->rc->config->get('dont_override', array());
 
         // map config option name to kolab folder type annotation
         $opts = array(
             'drafts_mbox' => 'mail.drafts',
             'sent_mbox'   => 'mail.sentitems',
             'junk_mbox'   => 'mail.junkemail',
             'trash_mbox'  => 'mail.wastebasket',
         );
 
         // check if any of special folders has been changed
         foreach ($opts as $opt_name => $type) {
             $new = $args['prefs'][$opt_name];
             $old = $this->rc->config->get($opt_name);
             if (!strlen($new) || $new === $old || in_array($opt_name, $dont_override)) {
                 unset($opts[$opt_name]);
             }
         }
 
         if (empty($opts)) {
             return $args;
         }
 
         $folderdata = kolab_storage::folders_typedata();
 
         if (!is_array($folderdata)) {
              return $args;
         }
 
         foreach ($opts as $opt_name => $type) {
             $foldername = $args['prefs'][$opt_name];
 
             // get all folders of specified type
             $folders = array_intersect($folderdata, array($type));
 
             // folder already annotated with specified type
             if (!empty($folders[$foldername])) {
                 continue;
             }
 
             // set type to the new folder
             $this->set_folder_type($foldername, $type);
 
             // unset old folder(s) type annotation
             list($maintype, $subtype) = explode('.', $type);
             foreach (array_keys($folders) as $folder) {
                 $this->set_folder_type($folder, $maintype);
             }
         }
 
         return $args;
     }
 
     /**
      * Handler for ACL permissions listing (acl_rights_simple hook)
      *
      * This shall combine the write and delete permissions into one item for
      * groupware folders as updating groupware objects is an insert + delete operation.
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function acl_rights_simple($args)
     {
         if ($args['folder']) {
             list($type,) = $this->get_folder_type($args['folder']);
 
             // we're dealing with a groupware folder here...
             if ($type && $type !== 'mail') {
                 if ($args['rights']['write'] && $args['rights']['delete']) {
                     $write_perms = $args['rights']['write'] . $args['rights']['delete'];
                     $rw_perms    = $write_perms . $args['rights']['read'];
 
                     $args['rights']['write'] = $write_perms;
                     $args['rights']['other'] = preg_replace("/[$rw_perms]/", '', $args['rights']['other']);
 
                     // add localized labels and titles for the altered items
                     $args['labels'] = array(
                         'other'  => $this->rc->gettext('shortacla','acl'),
                     );
                     $args['titles'] = array(
                         'other'  => $this->rc->gettext('longaclother','acl'),
                     );
                 }
             }
         }
 
         return $args;
     }
 
     /**
      * Handler for ACL permissions listing (acl_rights_supported hook)
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function acl_rights_supported($args)
     {
         if ($args['folder']) {
             list($type,) = $this->get_folder_type($args['folder']);
 
             // we're dealing with a groupware folder here...
             if ($type && $type !== 'mail') {
                 // remove some irrelevant (for groupware objects) rights
                 $args['rights'] = str_split(preg_replace('/[p]/', '', join('', $args['rights'])));
             }
         }
 
         return $args;
     }
 
     /**
      * Checks if IMAP server supports any of METADATA, ANNOTATEMORE, ANNOTATEMORE2
      *
      * @return bool
      */
     function metadata_support()
     {
         $storage = $this->rc->get_storage();
 
         return $storage->get_capability('METADATA') ||
             $storage->get_capability('ANNOTATEMORE') ||
             $storage->get_capability('ANNOTATEMORE2');
     }
 
     /**
      * Checks if IMAP server supports any of METADATA, ANNOTATEMORE, ANNOTATEMORE2
      *
      * @param string $folder Folder name
      *
      * @return array Folder content-type
      */
     function get_folder_type($folder)
     {
         $type = explode('.', (string)kolab_storage::folder_type($folder));
 
         if (!isset($type[1])) {
             $type[1] = null;
         }
 
         return $type;
     }
 
     /**
      * Sets folder content-type.
      *
      * @param string $folder Folder name
      * @param string $type   Content type
      *
      * @return bool True on success
      */
     function set_folder_type($folder, $type = 'mail')
     {
         return kolab_storage::set_folder_type($folder, $type);
     }
 
     /**
      * Returns the name of default folder
      *
      * @param string $type Folder type
      *
      * @return string Folder name
      */
     function get_default_folder($type)
     {
         $folderdata = kolab_storage::folders_typedata();
 
         if (!is_array($folderdata)) {
             return null;
         }
 
         // get all folders of specified type
         $folderdata = array_intersect($folderdata, array($type.'.default'));
 
         return key($folderdata);
     }
 
     /**
      * Returns CSS class name for specified folder type
      *
      * @param string $type Folder type
      *
      * @return string Class name
      */
     static function folder_class_name($type)
     {
         if ($type && strpos($type, '.')) {
             list($ctype, $subtype) = explode('.', $type);
 
             return 'type-' . $ctype . ' subtype-' . $subtype;
         }
 
         return 'type-' . ($type ? $type : 'mail');
     }
 
     /**
      * Creates default folders if they doesn't exist
      */
     private function create_default_folders(&$folders, $filter, $folderdata = null, $lsub = false)
     {
         $storage     = $this->rc->get_storage();
         $namespace   = $storage->get_namespace();
         $defaults    = array();
         $prefix      = '';
 
         // Find personal namespace prefix
         if (is_array($namespace['personal']) && count($namespace['personal']) == 1) {
             $prefix = $namespace['personal'][0][0];
         }
 
         $this->load_config();
 
         // get configured defaults
         foreach ($this->types as $type) {
             foreach ((array)$this->subtypes[$type] as $subtype) {
                 $opt_name = 'kolab_folders_' . $type . '_' . $subtype;
                 if ($folder = $this->rc->config->get($opt_name)) {
                     // convert configuration value to UTF7-IMAP charset
                     $folder = rcube_charset::convert($folder, RCUBE_CHARSET, 'UTF7-IMAP');
                     // and namespace prefix if needed
                     if ($prefix && strpos($folder, $prefix) === false && $folder != 'INBOX') {
                         $folder = $prefix . $folder;
                     }
                     $defaults[$type . '.' . $subtype] = $folder;
                 }
             }
         }
 
         if (empty($defaults)) {
             return;
         }
 
         if ($folderdata === null) {
             $folderdata = kolab_storage::folders_typedata();
         }
 
         if (!is_array($folderdata)) {
             return;
         }
 
         // find default folders
         foreach ($defaults as $type => $foldername) {
             // get all folders of specified type
             $_folders = array_intersect($folderdata, array($type));
 
             // default folder found
             if (!empty($_folders)) {
                 continue;
             }
 
             list($type1, $type2) = explode('.', $type);
 
             $activate = in_array($type1, $this->act_types);
             $exists   = false;
             $result   = false;
 
             // check if folder exists
             if (!empty($folderdata[$foldername]) || $foldername == 'INBOX') {
                 $exists = true;
             }
             else if ((!$filter || $filter == $type1) && in_array($foldername, $folders)) {
                 // this assumes also that subscribed folder exists
                 $exists = true;
             }
             else {
                 $exists = $storage->folder_exists($foldername);
             }
 
             // create folder
             if (!$exists) {
                 $exists = $storage->create_folder($foldername);
             }
 
             // set type + subscribe + activate
             if ($exists) {
                 if ($result = kolab_storage::set_folder_type($foldername, $type)) {
                     // check if folder is subscribed
                     if ((!$filter || $filter == $type1) && $lsub && in_array($foldername, $folders)) {
                         // already subscribed
                         $subscribed = true;
                     }
                     else {
                         $subscribed = $storage->subscribe($foldername);
                     }
 
                     // activate folder
                     if ($activate) {
                         kolab_storage::folder_activate($foldername, true);
                     }
                 }
             }
 
             // add new folder to the result
             if ($result && (!$filter || $filter == $type1) && (!$lsub || $subscribed)) {
                 $folders[] = $foldername;
             }
         }
     }
 
     /**
      * Static getter for default folder of the given type
      *
      * @param string $type Folder type
      *
      * @return string Folder name
      */
     public static function default_folder($type)
     {
         return self::$instance->get_default_folder($type);
     }
 
     /**
      * Get /shared/vendor/cmu/cyrus-imapd/expire value
      *
      * @param string $folder IMAP folder name
      *
      * @return int|false The annotation value or False if not supported
      */
     private function get_expire_annotation($folder)
     {
         $storage = $this->rc->get_storage();
 
         if ($storage->get_vendor() != 'cyrus') {
             return false;
         }
 
         if (!strlen($folder)) {
             return 0;
         }
 
         $value = $storage->get_metadata($folder, $this->expire_annotation);
 
         if (is_array($value)) {
             return !empty($value[$folder]) ? intval($value[$folder][$this->expire_annotation] ?? 0) : 0;
         }
 
         return false;
     }
 
     /**
      * Add expiration time input to the form if supported
      */
     private function add_expire_input(&$form, $folder, $type = null)
     {
         if (($expire = $this->get_expire_annotation($folder)) !== false) {
             $post    = trim(rcube_utils::get_input_value('_expire', rcube_utils::INPUT_POST));
             $is_mail = empty($type) || preg_match('/^mail/i', $type);
             $label   = $this->gettext('xdays');
             $input   = new html_inputfield(array(
                     'id'       => '_kolabexpire',
                     'name'     => '_expire',
                     'size'     => 3,
                     'disabled' => !$is_mail
             ));
 
             if ($post && $is_mail) {
                 $expire = (int) $post;
             }
 
             if (strpos($label, '$') === 0) {
                 $label = str_replace('$x', '', $label);
                 $html  = $input->show($expire ?: '')
                     . html::span('input-group-append', html::span('input-group-text', rcube::Q($label)));
             }
             else {
                 $label = str_replace('$x', '', $label);
                 $html  = html::span('input-group-prepend', html::span('input-group-text', rcube::Q($label)))
                     . $input->show($expire ?: '');
             }
 
             $form['props']['fieldsets']['settings']['content']['kolabexpire'] = array(
                 'label' => $this->gettext('folderexpire'),
                 'value' => html::div('input-group', $html),
             );
         }
     }
 
     /**
      * Handler for various folders list widgets (hooks)
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function render_folderlist($args)
     {
         $storage  = $this->rc->get_storage();
         $ns_other = $storage->get_namespace('other');
         $is_fl    = $this->rc->plugins->is_processing('folders_list');
 
         foreach ((array) $ns_other as $root) {
             $delim  = $root[1];
             $prefix = rtrim($root[0], $delim);
             $length = strlen($prefix);
 
             if (!$length) {
                 continue;
             }
 
             // folders_list hook mode
             if ($is_fl) {
                 foreach ((array) $args['list'] as $folder_name => $folder) {
                     if (strpos($folder_name, $root[0]) === 0 && !substr_count($folder_name, $root[1], $length+1)) {
                         if ($name = kolab_storage::folder_id2user(substr($folder_name, $length+1), true)) {
                             $old     = $args['list'][$folder_name]['display'];
                             $content = $args['list'][$folder_name]['content'];
 
                             $name    = rcube::Q($name);
                             $content = str_replace(">$old<", ">$name<", $content);
 
                             $args['list'][$folder_name]['display'] = $name;
                             $args['list'][$folder_name]['content'] = $content;
                         }
                     }
                 }
 
                 // TODO: Re-sort the list
             }
             // render_* hooks mode
             else if (!empty($args['list'][$prefix]) && !empty($args['list'][$prefix]['folders'])) {
                 $map = array();
                 foreach ($args['list'][$prefix]['folders'] as $folder_name => $folder) {
                     if ($name = kolab_storage::folder_id2user($folder_name, true)) {
                         $args['list'][$prefix]['folders'][$folder_name]['name'] = $name;
                     }
 
                     $map[$folder_name] = $name ?: $args['list'][$prefix]['folders'][$folder_name]['name'];
                 }
 
                 // Re-sort the list
                 uasort($map, 'strcoll');
                 $args['list'][$prefix]['folders'] = array_replace($map, $args['list'][$prefix]['folders']);
             }
         }
 
         return $args;
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage.php b/plugins/libkolab/lib/kolab_storage.php
index 893af60b..9f4791e5 100644
--- a/plugins/libkolab/lib/kolab_storage.php
+++ b/plugins/libkolab/lib/kolab_storage.php
@@ -1,1823 +1,1823 @@
 <?php
 
 /**
  * Kolab storage class providing static methods to access groupware objects on a Kolab server.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2012-2014, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage
 {
     const CTYPE_KEY         = '/shared/vendor/kolab/folder-type';
     const CTYPE_KEY_PRIVATE = '/private/vendor/kolab/folder-type';
     const COLOR_KEY_SHARED  = '/shared/vendor/kolab/color';
     const COLOR_KEY_PRIVATE = '/private/vendor/kolab/color';
     const NAME_KEY_SHARED   = '/shared/vendor/kolab/displayname';
     const NAME_KEY_PRIVATE  = '/private/vendor/kolab/displayname';
     const UID_KEY_SHARED    = '/shared/vendor/kolab/uniqueid';
     const UID_KEY_CYRUS     = '/shared/vendor/cmu/cyrus-imapd/uniqueid';
 
     const ERROR_IMAP_CONN      = 1;
     const ERROR_CACHE_DB       = 2;
     const ERROR_NO_PERMISSION  = 3;
     const ERROR_INVALID_FOLDER = 4;
 
     public static $version = '3.0';
     public static $last_error;
     public static $encode_ids = false;
 
     private static $ready = false;
     private static $with_tempsubs = true;
     private static $subscriptions;
     private static $ldapcache = array();
     private static $ldap = array();
     private static $states;
     private static $config;
     private static $imap;
 
 
     // Default folder names
     private static $default_folders = array(
         'event'         => 'Calendar',
         'contact'       => 'Contacts',
         'task'          => 'Tasks',
         'note'          => 'Notes',
         'file'          => 'Files',
         'configuration' => 'Configuration',
         'journal'       => 'Journal',
         'mail.inbox'       => 'INBOX',
         'mail.drafts'      => 'Drafts',
         'mail.sentitems'   => 'Sent',
         'mail.wastebasket' => 'Trash',
         'mail.outbox'      => 'Outbox',
         'mail.junkemail'   => 'Junk',
     );
 
 
     /**
      * Setup the environment needed by the libs
      */
     public static function setup()
     {
         if (self::$ready)
             return true;
 
         $rcmail = rcube::get_instance();
         self::$config  = $rcmail->config;
         self::$version = strval($rcmail->config->get('kolab_format_version', self::$version));
         self::$imap    = $rcmail->get_storage();
         self::$ready   = class_exists('kolabformat') &&
             (self::$imap->get_capability('METADATA') || self::$imap->get_capability('ANNOTATEMORE') || self::$imap->get_capability('ANNOTATEMORE2'));
 
         if (self::$ready) {
             // do nothing
         }
         else if (!class_exists('kolabformat')) {
             rcube::raise_error(array(
                 'code' => 900, 'type' => 'php',
                 'message' => "required kolabformat module not found"
             ), true);
         }
         else if (self::$imap->get_error_code()) {
             rcube::raise_error(array(
                 'code' => 900, 'type' => 'php', 'message' => "IMAP error"
             ), true);
         }
 
         // adjust some configurable settings
         if ($event_scheduling_prop = $rcmail->config->get('kolab_event_scheduling_properties', null)) {
             kolab_format_event::$scheduling_properties = (array)$event_scheduling_prop;
         }
         // adjust some configurable settings
         if ($task_scheduling_prop = $rcmail->config->get('kolab_task_scheduling_properties', null)) {
             kolab_format_task::$scheduling_properties = (array)$task_scheduling_prop;
         }
 
         return self::$ready;
     }
 
     /**
      * Initializes LDAP object to resolve Kolab users
      *
      * @param string $name Name of the configuration option with LDAP config
      */
     public static function ldap($name = 'kolab_users_directory')
     {
         self::setup();
 
         $config = self::$config->get($name);
 
         if (empty($config)) {
             $name   = 'kolab_auth_addressbook';
             $config = self::$config->get($name);
         }
 
         if (!empty(self::$ldap[$name])) {
             return self::$ldap[$name];
         }
 
         if (!is_array($config)) {
             $ldap_config = (array)self::$config->get('ldap_public');
             $config = $ldap_config[$config];
         }
 
         if (empty($config)) {
             return null;
         }
 
         $ldap = new kolab_ldap($config);
 
         // overwrite filter option
         if ($filter = self::$config->get('kolab_users_filter')) {
             self::$config->set('kolab_auth_filter', $filter);
         }
 
         $user_field = $user_attrib = self::$config->get('kolab_users_id_attrib');
 
         // Fallback to kolab_auth_login, which is not attribute, but field name
         if (!$user_field && ($user_field = self::$config->get('kolab_auth_login', 'email'))) {
             $user_attrib = $config['fieldmap'][$user_field];
         }
 
         if ($user_field && $user_attrib) {
             $ldap->extend_fieldmap(array($user_field => $user_attrib));
         }
 
         self::$ldap[$name] = $ldap;
 
         return $ldap;
     }
 
     /**
      * Get a list of storage folders for the given data type
      *
      * @param string Data type to list folders for (contact,distribution-list,event,task,note)
      * @param bool   Enable to return subscribed folders only (null to use configured subscription mode)
      *
      * @return array List of Kolab_Folder objects (folder names in UTF7-IMAP)
      */
     public static function get_folders($type, $subscribed = null)
     {
         $folders = $folderdata = array();
 
         if (self::setup()) {
             foreach ((array)self::list_folders('', '*', $type, $subscribed, $folderdata) as $foldername) {
                 $folders[$foldername] = new kolab_storage_folder($foldername, $type, $folderdata[$foldername]);
             }
         }
 
         return $folders;
     }
 
     /**
      * Getter for the storage folder for the given type
      *
      * @param string Data type to list folders for (contact,distribution-list,event,task,note)
      * @return object kolab_storage_folder  The folder object
      */
     public static function get_default_folder($type)
     {
         if (self::setup()) {
             foreach ((array)self::list_folders('', '*', $type . '.default', false, $folderdata) as $foldername) {
                 return new kolab_storage_folder($foldername, $type, $folderdata[$foldername]);
             }
         }
 
         return null;
     }
 
     /**
      * Getter for a specific storage folder
      *
      * @param string IMAP folder to access (UTF7-IMAP)
      * @param string Expected folder type
      *
      * @return object kolab_storage_folder  The folder object
      */
     public static function get_folder($folder, $type = null)
     {
         return self::setup() ? new kolab_storage_folder($folder, $type) : null;
     }
 
     /**
      * Getter for a single Kolab object, identified by its UID.
      * This will search all folders storing objects of the given type.
      *
      * @param string Object UID
      * @param string Object type (contact,event,task,journal,file,note,configuration)
      * @return array The Kolab object represented as hash array or false if not found
      */
     public static function get_object($uid, $type)
     {
         self::setup();
         $folder = null;
         foreach ((array)self::list_folders('', '*', $type, null, $folderdata) as $foldername) {
             if (!$folder)
                 $folder = new kolab_storage_folder($foldername, $type, $folderdata[$foldername]);
             else
                 $folder->set_folder($foldername, $type, $folderdata[$foldername]);
 
             if ($object = $folder->get_object($uid))
                 return $object;
         }
 
         return false;
     }
 
     /**
      * Execute cross-folder searches with the given query.
      *
      * @param array  Pseudo-SQL query as list of filter parameter triplets
      * @param string Folder type (contact,event,task,journal,file,note,configuration)
      * @param int    Expected number of records or limit (for performance reasons)
      *
      * @return array List of Kolab data objects (each represented as hash array)
      * @see kolab_storage_format::select()
      */
     public static function select($query, $type, $limit = null)
     {
         self::setup();
         $folder = null;
         $result = array();
 
         foreach ((array)self::list_folders('', '*', $type, null, $folderdata) as $foldername) {
             $folder = new kolab_storage_folder($foldername, $type, $folderdata[$foldername]);
 
             if ($limit) {
                 $folder->set_order_and_limit(null, $limit);
             }
 
             foreach ($folder->select($query) as $object) {
                 $result[] = $object;
             }
         }
 
         return $result;
     }
 
     /**
      * Returns Free-busy server URL
      */
     public static function get_freebusy_server()
     {
         $rcmail = rcube::get_instance();
 
         if ($url = $rcmail->config->get('kolab_freebusy_server')) {
             $url = rcube_utils::resolve_url($url);
             $url = unslashify($url);
         }
 
         return $url;
     }
 
     /**
      * Compose an URL to query the free/busy status for the given user
      *
      * @param string Email address of the user to get free/busy data for
      * @param object DateTime Start of the query range (optional)
      * @param object DateTime End of the query range (optional)
      *
      * @return ?string Fully qualified URL to query free/busy data
      */
     public static function get_freebusy_url($email, $start = null, $end = null)
     {
         $url = self::get_freebusy_server();
 
         if (empty($url)) {
             return null;
         }
 
         $query = '';
         $param = array();
         $utc = new \DateTimeZone('UTC');
 
         // https://www.calconnect.org/pubdocs/CD0903%20Freebusy%20Read%20URL.pdf
 
         if ($start instanceof \DateTime) {
             $start->setTimezone($utc);
             $param['start'] = $param['dtstart'] = $start->format('Ymd\THis\Z');
         }
 
         if ($end instanceof \DateTime) {
             $end->setTimezone($utc);
             $param['end'] = $param['dtend'] = $end->format('Ymd\THis\Z');
         }
 
         if (!empty($param)) {
             $query = '?' . http_build_query($param);
         }
 
         if (strpos($url, '%u')) {
             // Expected configured full URL, just replace the %u variable
             // Note: Cyrus v3 Free-Busy service does not use .ifb extension
             $url = str_replace('%u', rawurlencode($email), $url);
         }
         else {
             $url .= '/' . $email . '.ifb';
         }
 
         return $url . $query;
     }
 
     /**
      * Creates folder ID from folder name
      *
      * @param string $folder Folder name (UTF7-IMAP)
      * @param bool   $enc    Use lossless encoding
      *
      * @return string Folder ID string
      */
     public static function folder_id($folder, $enc = null)
     {
         return $enc == true || ($enc === null && self::$encode_ids) ?
             self::id_encode($folder) :
             asciiwords(strtr($folder, '/.-', '___'));
     }
 
     /**
      * Encode the given ID to a safe ascii representation
      *
      * @param string $id Arbitrary identifier string
      *
      * @return string Ascii representation
      */
     public static function id_encode($id)
     {
         return rtrim(strtr(base64_encode($id), '+/', '-_'), '=');
     }
 
     /**
      * Convert the given identifier back to it's raw value
      *
      * @param string $id Ascii identifier
      * @return string Raw identifier string
      */
     public static function id_decode($id)
     {
       return base64_decode(str_pad(strtr($id, '-_', '+/'), strlen($id) % 4, '=', STR_PAD_RIGHT));
     }
 
     /**
      * Return the (first) path of the requested IMAP namespace
      *
      * @param string  Namespace name (personal, shared, other)
      * @return string IMAP root path for that namespace
      */
     public static function namespace_root($name)
     {
         self::setup();
 
         foreach ((array)self::$imap->get_namespace($name) as $paths) {
             if (strlen($paths[0]) > 1) {
                 return $paths[0];
             }
         }
 
         return '';
     }
 
     /**
      * Deletes IMAP folder
      *
      * @param string $name Folder name (UTF7-IMAP)
      *
      * @return bool True on success, false on failure
      */
     public static function folder_delete($name)
     {
         // clear cached entries first
         if ($folder = self::get_folder($name))
             $folder->cache->purge();
 
         $rcmail = rcube::get_instance();
         $plugin = $rcmail->plugins->exec_hook('folder_delete', array('name' => $name));
 
         $success = self::$imap->delete_folder($name);
         self::$last_error = self::$imap->get_error_str();
 
         return $success;
     }
 
     /**
      * Creates IMAP folder
      *
      * @param string $name       Folder name (UTF7-IMAP)
      * @param string $type       Folder type
      * @param bool   $subscribed Sets folder subscription
      * @param bool   $active     Sets folder state (client-side subscription)
      *
      * @return bool True on success, false on failure
      */
     public static function folder_create($name, $type = null, $subscribed = false, $active = false)
     {
         self::setup();
 
         $rcmail = rcube::get_instance();
         $plugin = $rcmail->plugins->exec_hook('folder_create', array('record' => array(
             'name' => $name,
             'subscribe' => $subscribed,
         )));
 
         if ($saved = self::$imap->create_folder($name, $subscribed)) {
             // set metadata for folder type
             if ($type) {
                 $saved = self::set_folder_type($name, $type);
 
                 // revert if metadata could not be set
                 if (!$saved) {
                     self::$imap->delete_folder($name);
                 }
                 // activate folder
                 else if ($active) {
                     self::set_state($name, true);
                 }
             }
         }
 
         if ($saved) {
             return true;
         }
 
         self::$last_error = self::$imap->get_error_str();
         return false;
     }
 
     /**
      * Renames IMAP folder
      *
      * @param string $oldname Old folder name (UTF7-IMAP)
      * @param string $newname New folder name (UTF7-IMAP)
      *
      * @return bool True on success, false on failure
      */
     public static function folder_rename($oldname, $newname)
     {
         self::setup();
 
         $rcmail = rcube::get_instance();
         $plugin = $rcmail->plugins->exec_hook('folder_rename', array(
             'oldname' => $oldname, 'newname' => $newname));
 
         $oldfolder = self::get_folder($oldname);
         $active    = self::folder_is_active($oldname);
         $success   = self::$imap->rename_folder($oldname, $newname);
         self::$last_error = self::$imap->get_error_str();
 
         // pass active state to new folder name
         if ($success && $active) {
             self::set_state($oldname, false);
             self::set_state($newname, true);
         }
 
         // assign existing cache entries to new resource uri
         if ($success && $oldfolder) {
             $oldfolder->cache->rename($newname);
         }
 
         return $success;
     }
 
     /**
      * Rename or Create a new IMAP folder.
      *
      * Does additional checks for permissions and folder name restrictions
      *
      * @param array &$prop Hash array with folder properties and metadata
      *  - name:       Folder name
      *  - oldname:    Old folder name when changed
      *  - parent:     Parent folder to create the new one in
      *  - type:       Folder type to create
      *  - subscribed: Subscribed flag (IMAP subscription)
      *  - active:     Activation flag (client-side subscription)
      *
      * @return string|false New folder name or False on failure
      *
      * @see self::set_folder_props() for list of other properties
      */
     public static function folder_update(&$prop)
     {
         self::setup();
 
         $folder    = rcube_charset::convert($prop['name'], RCUBE_CHARSET, 'UTF7-IMAP');
         $oldfolder = $prop['oldname']; // UTF7
         $parent    = $prop['parent']; // UTF7
         $delimiter = self::$imap->get_hierarchy_delimiter();
 
         if (strlen($oldfolder)) {
             $options = self::$imap->folder_info($oldfolder);
         }
 
         if (!empty($options) && ($options['norename'] || $options['protected'])) {
         }
         // sanity checks (from steps/settings/save_folder.inc)
         else if (!strlen($folder)) {
             self::$last_error = 'cannotbeempty';
             return false;
         }
         else if (strlen($folder) > 128) {
             self::$last_error = 'nametoolong';
             return false;
         }
         else {
             // these characters are problematic e.g. when used in LIST/LSUB
             foreach (array($delimiter, '%', '*') as $char) {
                 if (strpos($folder, $char) !== false) {
                     self::$last_error = 'forbiddencharacter';
                     return false;
                 }
             }
         }
 
-        if (!empty($options) && ($options['protected'] || $options['norename'])) {
+        if (!empty($options) && (!empty($options['protected']) || !empty($options['norename']))) {
             $folder = $oldfolder;
         }
         else if (strlen($parent)) {
             $folder = $parent . $delimiter . $folder;
         }
         else {
             // add namespace prefix (when needed)
             $folder = self::$imap->mod_folder($folder, 'in');
         }
 
         // Check access rights to the parent folder
         if (strlen($parent) && (!strlen($oldfolder) || $oldfolder != $folder)) {
             $parent_opts = self::$imap->folder_info($parent);
             if ($parent_opts['namespace'] != 'personal'
                 && (empty($parent_opts['rights']) || !preg_match('/[ck]/', implode($parent_opts['rights'])))
             ) {
                 self::$last_error = 'No permission to create folder';
                 return false;
             }
         }
 
         // update the folder name
         if (strlen($oldfolder)) {
             if ($oldfolder != $folder) {
                 $result = self::folder_rename($oldfolder, $folder);
             }
             else {
                 $result = true;
             }
         }
         // create new folder
         else {
             $result = self::folder_create($folder, $prop['type'], $prop['subscribed'], $prop['active']);
         }
 
         if ($result) {
             self::set_folder_props($folder, $prop);
         }
 
         return $result ? $folder : false;
     }
 
     /**
      * Getter for human-readable name of Kolab object (folder)
      * with kolab_custom_display_names support.
      * See http://wiki.kolab.org/UI-Concepts/Folder-Listing for reference
      *
      * @param string $folder    IMAP folder name (UTF7-IMAP)
      * @param string $folder_ns Will be set to namespace name of the folder
      *
      * @return string Name of the folder-object
      */
     public static function object_name($folder, &$folder_ns=null)
     {
         // find custom display name in folder METADATA
         if ($name = self::custom_displayname($folder)) {
             return $name;
         }
 
         return self::object_prettyname($folder, $folder_ns);
     }
 
     /**
      * Get custom display name (saved in metadata) for the given folder
      */
     public static function custom_displayname($folder)
     {
         static $_metadata;
 
         // find custom display name in folder METADATA
         if (self::$config->get('kolab_custom_display_names', true) && self::setup()) {
             if ($_metadata !== null) {
                 $metadata = $_metadata;
             }
             else {
                 // For performance reasons ask for all folders, it will be cached as one cache entry
                 $metadata = self::$imap->get_metadata("*", [self::NAME_KEY_PRIVATE, self::NAME_KEY_SHARED]);
 
                 // If cache is disabled store result in memory
                 if (!self::$config->get('imap_cache')) {
                     $_metadata = $metadata;
                 }
             }
 
             if ($data = $metadata[$folder] ?? null) {
                 if (($name = $data[self::NAME_KEY_PRIVATE]) || ($name = $data[self::NAME_KEY_SHARED])) {
                     return $name;
                 }
             }
         }
 
         return false;
     }
 
     /**
      * Getter for human-readable name of Kolab object (folder)
      * See http://wiki.kolab.org/UI-Concepts/Folder-Listing for reference
      *
      * @param string $folder    IMAP folder name (UTF7-IMAP)
      * @param string $folder_ns Will be set to namespace name of the folder
      *
      * @return string Name of the folder-object
      */
     public static function object_prettyname($folder, &$folder_ns = null)
     {
         self::setup();
 
         $found     = false;
         $namespace = self::$imap->get_namespace();
         $prefix    = null;
 
         if (!empty($namespace['shared'])) {
             foreach ($namespace['shared'] as $ns) {
                 if (strlen($ns[0]) && strpos($folder, $ns[0]) === 0) {
                     $prefix = '';
                     $folder = substr($folder, strlen($ns[0]));
                     $delim  = $ns[1];
                     $found  = true;
                     $folder_ns = 'shared';
                     break;
                 }
             }
         }
 
         if (!$found && !empty($namespace['other'])) {
             foreach ($namespace['other'] as $ns) {
                 if (strlen($ns[0]) && strpos($folder, $ns[0]) === 0) {
                     // remove namespace prefix and extract username
                     $folder = substr($folder, strlen($ns[0]));
                     $delim  = $ns[1];
 
                     // get username part and map it to user name
                     $pos = strpos($folder, $delim);
                     $fid = $pos ? substr($folder, 0, $pos) : $folder;
 
                     if ($user = self::folder_id2user($fid, true)) {
                         $fid = str_replace($delim, '', $user);
                     }
 
                     $prefix = "($fid)";
                     $folder = $pos ? substr($folder, $pos + 1) : '';
                     $found  = true;
                     $folder_ns = 'other';
                     break;
                 }
             }
         }
 
         if (!$found && !empty($namespace['personal'])) {
             foreach ($namespace['personal'] as $ns) {
                 if (strlen($ns[0]) && strpos($folder, $ns[0]) === 0) {
                     // remove namespace prefix
                     $folder = substr($folder, strlen($ns[0]));
                     $prefix = '';
                     $delim  = $ns[1];
                     $found  = true;
                     break;
                 }
             }
         }
 
         if (empty($delim)) {
             $delim = self::$imap->get_hierarchy_delimiter();
         }
 
         $folder = rcube_charset::convert($folder, 'UTF7-IMAP');
         $folder = html::quote($folder);
         $folder = str_replace(html::quote($delim), ' &raquo; ', $folder);
 
         if ($prefix) {
             $folder = html::quote($prefix) . ($folder !== '' ? ' ' . $folder : '');
         }
 
         if (empty($folder_ns)) {
             $folder_ns = 'personal';
         }
 
         return $folder;
     }
 
     /**
      * Helper method to generate a truncated folder name to display.
      * Note: $origname is a string returned by self::object_name()
      */
     public static function folder_displayname($origname, &$names)
     {
         $name = $origname;
 
         // find folder prefix to truncate
         for ($i = count($names)-1; $i >= 0; $i--) {
             if (strpos($name, $names[$i] . ' &raquo; ') === 0) {
                 $length = strlen($names[$i] . ' &raquo; ');
                 $prefix = substr($name, 0, $length);
                 $count  = count(explode(' &raquo; ', $prefix));
                 $diff   = 1;
 
                 // check if prefix folder is in other users namespace
                 for ($n = count($names)-1; $n >= 0; $n--) {
                     if (strpos($prefix, '(' . $names[$n] . ') ') === 0) {
                         $diff = 0;
                         break;
                     }
                 }
 
                 $name = str_repeat('&nbsp;&nbsp;&nbsp;', $count - $diff) . '&raquo; ' . substr($name, $length);
                 break;
             }
             // other users namespace and parent folder exists
             else if (strpos($name, '(' . $names[$i] . ') ') === 0) {
                 $length = strlen('(' . $names[$i] . ') ');
                 $prefix = substr($name, 0, $length);
                 $count  = count(explode(' &raquo; ', $prefix));
                 $name   = str_repeat('&nbsp;&nbsp;&nbsp;', $count) . '&raquo; ' . substr($name, $length);
                 break;
             }
         }
 
         $names[] = $origname;
 
         return $name;
     }
 
     /**
      * Creates a SELECT field with folders list
      *
      * @param string $type    Folder type
      * @param array  $attrs   SELECT field attributes (e.g. name)
      * @param string $current The name of current folder (to skip it)
      *
      * @return html_select SELECT object
      */
     public static function folder_selector($type, $attrs, $current = '')
     {
         // get all folders of specified type (sorted)
         $folders = self::get_folders($type, true);
 
         $delim = self::$imap->get_hierarchy_delimiter();
         $names = array();
         $len   = strlen($current);
 
         if ($len && ($rpos = strrpos($current, $delim))) {
             $parent = substr($current, 0, $rpos);
             $p_len  = strlen($parent);
         }
 
         // Filter folders list
         foreach ($folders as $c_folder) {
             $name = $c_folder->name;
 
             // skip current folder and it's subfolders
             if ($len) {
                 if ($name == $current) {
                     // Make sure parent folder is listed (might be skipped e.g. if it's namespace root)
                     if ($p_len && !isset($names[$parent])) {
                         $names[$parent] = self::object_name($parent);
                     }
                     continue;
                 }
                 if (strpos($name, $current.$delim) === 0) {
                     continue;
                 }
             }
 
             // always show the parent of current folder
             if ($p_len && $name == $parent) {
             }
             // skip folders where user have no rights to create subfolders
             else if ($c_folder->get_owner() != $_SESSION['username']) {
                 $rights = $c_folder->get_myrights();
                 if (!preg_match('/[ck]/', $rights)) {
                     continue;
                 }
             }
 
             $names[$name] = $c_folder->get_name();
         }
 
         // Build SELECT field of parent folder
         $attrs['is_escaped'] = true;
         $select = new html_select($attrs);
         $select->add('---', '');
 
         $listnames = array();
         foreach (array_keys($names) as $imap_name) {
             $name = $origname = $names[$imap_name];
 
             // find folder prefix to truncate
             for ($i = count($listnames)-1; $i >= 0; $i--) {
                 if (strpos($name, $listnames[$i].' &raquo; ') === 0) {
                     $length = strlen($listnames[$i].' &raquo; ');
                     $prefix = substr($name, 0, $length);
                     $count  = count(explode(' &raquo; ', $prefix));
                     $name   = str_repeat('&nbsp;&nbsp;', $count-1) . '&raquo; ' . substr($name, $length);
                     break;
                 }
             }
 
             $listnames[] = $origname;
             $select->add($name, $imap_name);
         }
 
         return $select;
     }
 
     /**
      * Returns a list of folder names
      *
      * @param string  Optional root folder
      * @param string  Optional name pattern
      * @param string  Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param bool    Enable to return subscribed folders only (null to use configured subscription mode)
      * @param array   Will be filled with folder-types data
      *
      * @return array List of folders
      */
     public static function list_folders($root = '', $mbox = '*', $filter = null, $subscribed = null, &$folderdata = array())
     {
         if (!self::setup()) {
             return null;
         }
 
         // use IMAP subscriptions
         if ($subscribed === null && self::$config->get('kolab_use_subscriptions')) {
             $subscribed = true;
         }
 
         if (!$filter) {
             // Get ALL folders list, standard way
             if ($subscribed) {
                 $folders = self::_imap_list_subscribed($root, $mbox, $filter);
             }
             else {
                 $folders = self::_imap_list_folders($root, $mbox);
             }
 
             return $folders;
         }
         $prefix = $root . $mbox;
         $regexp = '/^' . preg_quote($filter, '/') . '(\..+)?$/';
 
         // get folders types for all folders
         $folderdata = self::folders_typedata($prefix);
 
         if (!is_array($folderdata)) {
             return array();
         }
 
         // If we only want groupware folders and don't care about the subscription state,
         // then the metadata will already contain all folder names and we can avoid the LIST below.
         if (!$subscribed && $filter != 'mail' && $prefix == '*') {
             foreach ($folderdata as $folder => $type) {
                 if (!preg_match($regexp, (string) $type)) {
                     unset($folderdata[$folder]);
                 }
             }
 
             return self::$imap->sort_folder_list(array_keys($folderdata), true);
         }
 
         // Get folders list
         if ($subscribed) {
             $folders = self::_imap_list_subscribed($root, $mbox, $filter);
         }
         else {
             $folders = self::_imap_list_folders($root, $mbox);
         }
 
         // In case of an error, return empty list (?)
         if (!is_array($folders)) {
             return array();
         }
 
         // Filter folders list
         foreach ($folders as $idx => $folder) {
             $type = $folderdata[$folder] ?? null;
 
             if ($filter == 'mail' && empty($type)) {
                 continue;
             }
 
             if (empty($type) || !preg_match($regexp, $type)) {
                 unset($folders[$idx]);
             }
         }
 
         return $folders;
     }
 
     /**
      * Wrapper for rcube_imap::list_folders() with optional post-filtering
      */
     protected static function _imap_list_folders($root, $mbox)
     {
         $postfilter = null;
 
         // compose a post-filter expression for the excluded namespaces
         if ($root . $mbox == '*' && ($skip_ns = self::$config->get('kolab_skip_namespace'))) {
             $excludes = array();
             foreach ((array)$skip_ns as $ns) {
                 if ($ns_root = self::namespace_root($ns)) {
                     $excludes[] = $ns_root;
                 }
             }
 
             if (count($excludes)) {
                 $postfilter = '!^(' . join(')|(', array_map('preg_quote', $excludes)) . ')!';
             }
         }
 
         // use normal LIST command to return all folders, it's fast enough
         $folders = self::$imap->list_folders($root, $mbox, null, null, !empty($postfilter));
 
         if (!empty($postfilter)) {
             $folders = array_filter($folders, function($folder) use ($postfilter) { return !preg_match($postfilter, $folder); });
             $folders = self::$imap->sort_folder_list($folders);
         }
 
         return $folders;
     }
 
     /**
      * Wrapper for rcube_imap::list_folders_subscribed()
      * with support for temporarily subscribed folders
      */
     protected static function _imap_list_subscribed($root, $mbox, $filter = null)
     {
         $folders = self::$imap->list_folders_subscribed($root, $mbox);
 
         // add temporarily subscribed folders
         if ($filter != 'mail' && self::$with_tempsubs && is_array($_SESSION['kolab_subscribed_folders'] ?? null)) {
             $folders = array_unique(array_merge($folders, $_SESSION['kolab_subscribed_folders']));
         }
 
         return $folders;
     }
 
     /**
      * Search for shared or otherwise not listed groupware folders the user has access
      *
      * @param string Folder type of folders to search for
      * @param string Search string
      * @param array  Namespace(s) to exclude results from
      *
      * @return array List of matching kolab_storage_folder objects
      */
     public static function search_folders($type, $query, $exclude_ns = array())
     {
         if (!self::setup()) {
             return array();
         }
 
         $folders = array();
         $query = str_replace('*', '', $query);
 
         // find unsubscribed IMAP folders of the given type
         foreach ((array)self::list_folders('', '*', $type, false, $folderdata) as $foldername) {
             // FIXME: only consider the last part of the folder path for searching?
             $realname = strtolower(rcube_charset::convert($foldername, 'UTF7-IMAP'));
             if (($query == '' || strpos($realname, $query) !== false) &&
                 !self::folder_is_subscribed($foldername, true) &&
                 !in_array(self::$imap->folder_namespace($foldername), (array)$exclude_ns)
               ) {
                 $folders[] = new kolab_storage_folder($foldername, $type, $folderdata[$foldername]);
             }
         }
 
         return $folders;
     }
 
     /**
      * Sort the given list of kolab folders by namespace/name
      *
      * @param array List of kolab_storage_folder objects
      * @return array Sorted list of folders
      */
     public static function sort_folders($folders)
     {
         $pad     = '  ';
         $out     = array();
         $nsnames = array('personal' => array(), 'shared' => array(), 'other' => array());
 
         foreach ($folders as $folder) {
             $_folders[$folder->name] = $folder;
             $ns = $folder->get_namespace();
             $nsnames[$ns][$folder->name] = strtolower(html_entity_decode($folder->get_name(), ENT_COMPAT, RCUBE_CHARSET)) . $pad;  // decode &raquo;
         }
 
         // $folders is a result of get_folders() we can assume folders were already sorted
         foreach (array_keys($nsnames) as $ns) {
             asort($nsnames[$ns], SORT_LOCALE_STRING);
             foreach (array_keys($nsnames[$ns]) as $utf7name) {
                 $out[] = $_folders[$utf7name];
             }
         }
 
         return $out;
     }
 
     /**
      * Check the folder tree and add the missing parents as virtual folders
      *
      * @param array $folders Folders list
      * @param object $tree   Reference to the root node of the folder tree
      *
      * @return array Flat folders list
      */
     public static function folder_hierarchy($folders, &$tree = null)
     {
         if (!self::setup()) {
             return array();
         }
 
         $_folders = array();
         $delim    = self::$imap->get_hierarchy_delimiter();
         $other_ns = rtrim(self::namespace_root('other'), $delim);
         $tree     = new kolab_storage_folder_virtual('', '<root>', '');  // create tree root
         $refs     = array('' => $tree);
 
         foreach ($folders as $idx => $folder) {
             $path = explode($delim, $folder->name);
             array_pop($path);
             $folder->parent = join($delim, $path);
             $folder->children = array();  // reset list
 
             // skip top folders or ones with a custom displayname
             if (count($path) < 1 || kolab_storage::custom_displayname($folder->name)) {
                 $tree->children[] = $folder;
             }
             else {
                 $parents = array();
                 $depth = $folder->get_namespace() == 'personal' ? 1 : 2;
 
                 while (count($path) >= $depth && ($parent = join($delim, $path))) {
                     array_pop($path);
                     $parent_parent = join($delim, $path);
 
                     if (!$refs[$parent]) {
                         if ($folder->type && self::folder_type($parent) == $folder->type) {
                             $refs[$parent] = new kolab_storage_folder($parent, $folder->type, $folder->type);
                             $refs[$parent]->parent = $parent_parent;
                         }
                         else if ($parent_parent == $other_ns) {
                             $refs[$parent] = new kolab_storage_folder_user($parent, $parent_parent);
                         }
                         else {
                             $name = kolab_storage::object_name($parent);
                             $refs[$parent] = new kolab_storage_folder_virtual($parent, $name, $folder->get_namespace(), $parent_parent);
                         }
                         $parents[] = $refs[$parent];
                     }
                 }
 
                 if (!empty($parents)) {
                     $parents = array_reverse($parents);
                     foreach ($parents as $parent) {
-                        $parent_node = $refs[$parent->parent] ?: $tree;
+                        $parent_node = !empty($refs[$parent->parent]) ? $refs[$parent->parent] : $tree;
                         $parent_node->children[] = $parent;
                         $_folders[] = $parent;
                     }
                 }
 
-                $parent_node = $refs[$folder->parent] ?: $tree;
+                $parent_node = !empty($refs[$folder->parent]) ? $refs[$folder->parent] : $tree;
                 $parent_node->children[] = $folder;
             }
 
             $refs[$folder->name] = $folder;
             $_folders[] = $folder;
             unset($folders[$idx]);
         }
 
         return $_folders;
     }
 
     /**
      * Returns folder types indexed by folder name
      *
      * @param string $prefix Folder prefix (Default '*' for all folders)
      *
      * @return array|bool List of folders, False on failure
      */
     public static function folders_typedata($prefix = '*')
     {
         if (!self::setup()) {
             return false;
         }
 
         $type_keys = array(self::CTYPE_KEY, self::CTYPE_KEY_PRIVATE);
 
         // fetch metadata from *some* folders only
         if (($prefix == '*' || $prefix == '') && ($skip_ns = self::$config->get('kolab_skip_namespace'))) {
             $delimiter = self::$imap->get_hierarchy_delimiter();
             $folderdata = $blacklist = array();
             foreach ((array)$skip_ns as $ns) {
                 if ($ns_root = rtrim(self::namespace_root($ns), $delimiter)) {
                     $blacklist[] = $ns_root;
                 }
             }
             foreach (array('personal','other','shared') as $ns) {
                 if (!in_array($ns, (array)$skip_ns)) {
                     $ns_root = rtrim(self::namespace_root($ns), $delimiter);
 
                     // list top-level folders and their childs one by one
                     // GETMETADATA "%" doesn't list shared or other namespace folders but "*" would
                     if ($ns_root == '') {
                         foreach ((array)self::$imap->get_metadata('%', $type_keys) as $folder => $metadata) {
                             if (!in_array($folder, $blacklist)) {
                                 $folderdata[$folder] = $metadata;
                                 $opts = self::$imap->folder_attributes($folder);
                                 if (!in_array('\\HasNoChildren', $opts) && ($data = self::$imap->get_metadata($folder.$delimiter.'*', $type_keys))) {
                                     $folderdata += $data;
                                 }
                             }
                         }
                     }
                     else if ($data = self::$imap->get_metadata($ns_root.$delimiter.'*', $type_keys)) {
                         $folderdata += $data;
                     }
                 }
             }
         }
         else {
             $folderdata = self::$imap->get_metadata($prefix, $type_keys);
         }
 
         if (!is_array($folderdata)) {
             return false;
         }
 
         return array_map(array('kolab_storage', 'folder_select_metadata'), $folderdata);
     }
 
     /**
      * Callback for array_map to select the correct annotation value
      */
     public static function folder_select_metadata($types)
     {
         if (!empty($types[self::CTYPE_KEY_PRIVATE])) {
             return $types[self::CTYPE_KEY_PRIVATE];
         }
         else if (!empty($types[self::CTYPE_KEY])) {
             list($ctype, ) = explode('.', $types[self::CTYPE_KEY]);
             return $ctype;
         }
         return null;
     }
 
     /**
      * Returns type of IMAP folder
      *
      * @param string $folder Folder name (UTF7-IMAP)
      *
      * @return string Folder type
      */
     public static function folder_type($folder)
     {
         self::setup();
 
         $metadata = self::$imap->get_metadata($folder, array(self::CTYPE_KEY, self::CTYPE_KEY_PRIVATE));
 
         if (!is_array($metadata)) {
             return null;
         }
 
         if (!empty($metadata[$folder])) {
             return self::folder_select_metadata($metadata[$folder]);
         }
 
         return 'mail';
     }
 
     /**
      * Sets folder content-type.
      *
      * @param string $folder Folder name
      * @param string $type   Content type
      *
      * @return bool True on success
      */
     public static function set_folder_type($folder, $type = 'mail')
     {
         self::setup();
 
         list($ctype, $subtype) = strpos($type, '.') !== false ? explode('.', $type) : array($type, null);
 
         $success = self::$imap->set_metadata($folder, array(self::CTYPE_KEY => $ctype, self::CTYPE_KEY_PRIVATE => $subtype ? $type : null));
 
         if (!$success) {
             // fallback: only set private annotation
             $success |= self::$imap->set_metadata($folder, array(self::CTYPE_KEY_PRIVATE => $type));
         }
 
         return $success;
     }
 
     /**
      * Check subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp  Include temporary/session subscriptions
      *
      * @return bool True if subscribed, false if not
      */
     public static function folder_is_subscribed($folder, $temp = false)
     {
         if (self::$subscriptions === null) {
             self::setup();
             self::$with_tempsubs = false;
             self::$subscriptions = self::$imap->list_folders_subscribed();
             self::$with_tempsubs = true;
         }
 
         return in_array($folder, self::$subscriptions) ||
             ($temp && in_array($folder, (array)$_SESSION['kolab_subscribed_folders']));
     }
 
     /**
      * Change subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp   Only subscribe temporarily for the current session
      *
      * @return bool True on success, false on error
      */
     public static function folder_subscribe($folder, $temp = false)
     {
         self::setup();
 
         // temporary/session subscription
         if ($temp) {
             if (self::folder_is_subscribed($folder)) {
                 return true;
             }
             else if (empty($_SESSION['kolab_subscribed_folders']) || !in_array($folder, $_SESSION['kolab_subscribed_folders'])) {
                 $_SESSION['kolab_subscribed_folders'][] = $folder;
                 return true;
             }
         }
         else if (self::$imap->subscribe($folder)) {
             self::$subscriptions = null;
             return true;
         }
 
         return false;
     }
 
     /**
      * Change subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp   Only remove temporary subscription
      *
      * @return bool True on success, false on error
      */
     public static function folder_unsubscribe($folder, $temp = false)
     {
         self::setup();
 
         // temporary/session subscription
         if ($temp) {
             if (!empty($_SESSION['kolab_subscribed_folders']) && ($i = array_search($folder, $_SESSION['kolab_subscribed_folders'])) !== false) {
                 unset($_SESSION['kolab_subscribed_folders'][$i]);
             }
             return true;
         }
         else if (self::$imap->unsubscribe($folder)) {
             self::$subscriptions = null;
             return true;
         }
 
         return false;
     }
 
     /**
      * Check activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return bool True if active, false if not
      */
     public static function folder_is_active($folder)
     {
         $active_folders = self::get_states();
 
         return in_array($folder, $active_folders);
     }
 
     /**
      * Change activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return bool True on success, false on error
      */
     public static function folder_activate($folder)
     {
         // activation implies temporary subscription
         self::folder_subscribe($folder, true);
         return self::set_state($folder, true);
     }
 
     /**
      * Change activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return bool True on success, false on error
      */
     public static function folder_deactivate($folder)
     {
         // remove from temp subscriptions, really?
         self::folder_unsubscribe($folder, true);
 
         return self::set_state($folder, false);
     }
 
     /**
      * Return list of active folders
      */
     private static function get_states()
     {
         if (self::$states !== null) {
             return self::$states;
         }
 
         $rcube   = rcube::get_instance();
         $folders = $rcube->config->get('kolab_active_folders');
 
         if ($folders !== null) {
             self::$states = !empty($folders) ? explode('**', $folders) : array();
         }
         // for backward-compatibility copy server-side subscriptions to activation states
         else {
             self::setup();
             if (self::$subscriptions === null) {
                 self::$with_tempsubs = false;
                 self::$subscriptions = self::$imap->list_folders_subscribed();
                 self::$with_tempsubs = true;
             }
             self::$states = (array) self::$subscriptions;
             $folders = implode('**', self::$states);
             $rcube->user->save_prefs(array('kolab_active_folders' => $folders));
         }
 
         return self::$states;
     }
 
     /**
      * Update list of active folders
      */
     private static function set_state($folder, $state)
     {
         self::get_states();
 
         // update in-memory list
         $idx = array_search($folder, self::$states);
         if ($state && $idx === false) {
             self::$states[] = $folder;
         }
         else if (!$state && $idx !== false) {
             unset(self::$states[$idx]);
         }
 
         // update user preferences
         $folders = implode('**', self::$states);
 
         return rcube::get_instance()->user->save_prefs(array('kolab_active_folders' => $folders));
     }
 
     /**
      * Creates default folder of specified type
      * To be run when none of subscribed folders (of specified type) is found
      *
      * @param string $type  Folder type
      * @param string $props Folder properties (color, etc)
      *
      * @return string Folder name
      */
     public static function create_default_folder($type, $props = array())
     {
         if (!self::setup()) {
             return;
         }
 
         $folders = self::$imap->get_metadata('*', array(kolab_storage::CTYPE_KEY_PRIVATE));
 
         // from kolab_folders config
         $folder_type  = strpos($type, '.') ? str_replace('.', '_', $type) : $type . '_default';
         $default_name = self::$config->get('kolab_folders_' . $folder_type);
         $folder_type  = str_replace('_', '.', $folder_type);
 
         // check if we have any folder in personal namespace
         // folder(s) may exist but not subscribed
         foreach ((array)$folders as $f => $data) {
             if (strpos($data[self::CTYPE_KEY_PRIVATE], $type) === 0) {
                 $folder = $f;
                 break;
             }
         }
 
         if (!$folder) {
             if (!$default_name) {
                 $default_name = self::$default_folders[$type];
             }
 
             if (!$default_name) {
                 return;
             }
 
             $folder = rcube_charset::convert($default_name, RCUBE_CHARSET, 'UTF7-IMAP');
             $prefix = self::$imap->get_namespace('prefix');
 
             // add personal namespace prefix if needed
             if ($prefix && strpos($folder, $prefix) !== 0 && $folder != 'INBOX') {
                 $folder = $prefix . $folder;
             }
 
             if (!self::$imap->folder_exists($folder)) {
                 if (!self::$imap->create_folder($folder)) {
                     return;
                 }
             }
 
             self::set_folder_type($folder, $folder_type);
         }
 
         self::folder_subscribe($folder);
 
         if ($props['active']) {
             self::set_state($folder, true);
         }
 
         if (!empty($props)) {
             self::set_folder_props($folder, $props);
         }
 
         return $folder;
     }
 
     /**
      * Sets folder metadata properties
      *
      * @param string $folder Folder name
      * @param array  &$prop  Folder properties (color, displayname)
      */
     public static function set_folder_props($folder, &$prop)
     {
         if (!self::setup()) {
             return;
         }
 
         // TODO: also save 'showalarams' and other properties here
         $ns        = self::$imap->folder_namespace($folder);
         $supported = array(
             'color'       => array(self::COLOR_KEY_SHARED, self::COLOR_KEY_PRIVATE),
             'displayname' => array(self::NAME_KEY_SHARED, self::NAME_KEY_PRIVATE),
         );
 
         foreach ($supported as $key => $metakeys) {
             if (array_key_exists($key, $prop)) {
                 $meta_saved = false;
                 if ($ns == 'personal')  // save in shared namespace for personal folders
                     $meta_saved = self::$imap->set_metadata($folder, array($metakeys[0] => $prop[$key]));
                 if (!$meta_saved)    // try in private namespace
                     $meta_saved = self::$imap->set_metadata($folder, array($metakeys[1] => $prop[$key]));
                 if ($meta_saved)
                     unset($prop[$key]);  // unsetting will prevent fallback to local user prefs
             }
         }
     }
 
     /**
      * Search users in Kolab LDAP storage
      *
      * @param mixed   $query    Search value (or array of field => value pairs)
      * @param int     $mode     Matching mode: 0 - partial (*abc*), 1 - strict (=), 2 - prefix (abc*)
      * @param array   $required List of fields that shall ot be empty
      * @param int     $limit    Maximum number of records
      * @param int     $count    Returns the number of records found
      *
      * @return array List of users
      */
     public static function search_users($query, $mode = 1, $required = array(), $limit = 0, &$count = 0)
     {
         $query = str_replace('*', '', $query);
 
         // requires a working LDAP setup
         if (!strlen($query) || !($ldap = self::ldap())) {
             return array();
         }
 
         $root          = self::namespace_root('other');
         $user_attrib   = self::$config->get('kolab_users_id_attrib', self::$config->get('kolab_auth_login', 'mail'));
         $search_attrib = self::$config->get('kolab_users_search_attrib', array('cn','mail','alias'));
 
         // search users using the configured attributes
         $results = $ldap->dosearch($search_attrib, $query, $mode, $required, $limit, $count);
 
         // exclude myself
         if ($_SESSION['kolab_dn']) {
             unset($results[$_SESSION['kolab_dn']]);
         }
 
         // resolve to IMAP folder name
         array_walk($results, function(&$user, $dn) use ($root, $user_attrib) {
             list($localpart, ) = explode('@', $user[$user_attrib]);
             $user['kolabtargetfolder'] = $root . $localpart;
         });
 
         return $results;
     }
 
     /**
      * Returns a list of IMAP folders shared by the given user
      *
      * @param array   User entry from LDAP
      * @param string  Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param int     1 - subscribed folders only, 0 - all folders, 2 - all non-active
      * @param array   Will be filled with folder-types data
      *
      * @return array List of folders
      */
     public static function list_user_folders($user, $type, $subscribed = 0, &$folderdata = array())
     {
         self::setup();
 
         $folders = array();
 
         // use localpart of user attribute as root for folder listing
         $user_attrib = self::$config->get('kolab_users_id_attrib', self::$config->get('kolab_auth_login', 'mail'));
         if (!empty($user[$user_attrib])) {
             list($mbox) = explode('@', $user[$user_attrib]);
 
             $delimiter  = self::$imap->get_hierarchy_delimiter();
             $other_ns   = self::namespace_root('other');
             $prefix     = $other_ns . $mbox . $delimiter;
             $subscribed = (int) $subscribed;
             $subs       = $subscribed < 2 ? (bool) $subscribed : false;
             $folders    = self::list_folders($prefix, '*', $type, $subs, $folderdata);
 
             if ($subscribed === 2 && !empty($folders)) {
                 $active = self::get_states();
                 if (!empty($active)) {
                     $folders = array_diff($folders, $active);
                 }
             }
         }
 
         return $folders;
     }
 
     /**
      * Get a list of (virtual) top-level folders from the other users namespace
      *
      * @param string Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param bool   Enable to return subscribed folders only (null to use configured subscription mode)
      *
      * @return array List of kolab_storage_folder_user objects
      */
     public static function get_user_folders($type, $subscribed)
     {
         $folders = $folderdata = array();
 
         if (self::setup()) {
             $delimiter = self::$imap->get_hierarchy_delimiter();
             $other_ns = rtrim(self::namespace_root('other'), $delimiter);
             $path_len = count(explode($delimiter, $other_ns));
 
             foreach ((array) self::list_folders($other_ns . $delimiter, '*', '', $subscribed) as $foldername) {
                 if ($foldername == 'INBOX')  // skip INBOX which is added by default
                     continue;
 
                 $path = explode($delimiter, $foldername);
 
                 // compare folder type if a subfolder is listed
                 if ($type && count($path) > $path_len + 1 && $type != self::folder_type($foldername)) {
                     continue;
                 }
 
                 // truncate folder path to top-level folders of the 'other' namespace
                 $foldername = join($delimiter, array_slice($path, 0, $path_len + 1));
 
                 if (empty($folders[$foldername])) {
                     $folders[$foldername] = new kolab_storage_folder_user($foldername, $other_ns);
                 }
             }
 
             // for every (subscribed) user folder, list all (unsubscribed) subfolders
             foreach ($folders as $userfolder) {
                 foreach ((array) self::list_folders($userfolder->name . $delimiter, '*', $type, false, $folderdata) as $foldername) {
                     if (empty($folders[$foldername])) {
                         $folders[$foldername] = new kolab_storage_folder($foldername, $type, $folderdata[$foldername] ?? null);
                         $userfolder->children[] = $folders[$foldername];
                     }
                 }
             }
         }
 
         return $folders;
     }
 
     /**
      * Handler for user_delete plugin hooks
      *
      * Remove all cache data from the local database related to the given user.
      */
     public static function delete_user_folders($args)
     {
         $db = rcmail::get_instance()->get_dbh();
         $prefix = 'imap://' . urlencode($args['username']) . '@' . $args['host'] . '/%';
         $db->query("DELETE FROM " . $db->table_name('kolab_folders', true) . " WHERE `resource` LIKE ?", $prefix);
 
     }
 
     /**
      * Get folder METADATA for all supported keys
      * Do this in one go for better caching performance
      */
     public static function folder_metadata($folder)
     {
         if (self::setup()) {
             $keys = array(
                 // For better performance we skip displayname here, see (self::custom_displayname())
                 // self::NAME_KEY_PRIVATE,
                 // self::NAME_KEY_SHARED,
                 self::CTYPE_KEY,
                 self::CTYPE_KEY_PRIVATE,
                 self::COLOR_KEY_PRIVATE,
                 self::COLOR_KEY_SHARED,
                 self::UID_KEY_SHARED,
                 self::UID_KEY_CYRUS,
             );
 
             $metadata = self::$imap->get_metadata($folder, $keys);
 
             return $metadata[$folder];
         }
     }
 
     /**
      * Get user attributes for specified other user (imap) folder identifier.
      *
      * @param string $folder_id Folder name w/o path (imap user identifier)
      * @param bool   $as_string Return configured display name attribute value
      *
      * @return array User attributes
      * @see self::ldap()
      */
     public static function folder_id2user($folder_id, $as_string = false)
     {
         static $domain, $cache, $name_attr;
 
         $rcube = rcube::get_instance();
 
         if ($domain === null) {
             list(, $domain) = explode('@', $rcube->get_user_name());
         }
 
         if ($name_attr === null) {
             $name_attr = (array) ($rcube->config->get('kolab_users_name_field', $rcube->config->get('kolab_auth_name')) ?: 'name');
         }
 
         $token = $folder_id;
         if ($domain && strpos($token, '@') === false) {
             $token .= '@' . $domain;
         }
 
         if ($cache === null) {
             $cache = $rcube->get_cache_shared('kolab_users') ?: false;
         }
 
         // use value cached in memory for repeated lookups
         if (!$cache && array_key_exists($token, self::$ldapcache)) {
             $user = self::$ldapcache[$token];
         }
 
         if (empty($user) && $cache) {
             $user = $cache->get($token);
         }
 
         if (empty($user) && ($ldap = self::ldap())) {
             $user = $ldap->get_user_record($token, $_SESSION['imap_host']);
 
             if (!empty($user)) {
                 $keys = array('displayname', 'name', 'mail'); // supported keys
                 $user = array_intersect_key($user, array_flip($keys));
 
                 if (!empty($user)) {
                     if ($cache) {
                         $cache->set($token, $user);
                     }
                     else {
                         self::$ldapcache[$token] = $user;
                     }
                 }
             }
         }
 
         if (!empty($user)) {
             if ($as_string) {
                 foreach ($name_attr as $attr) {
                     if ($display = $user[$attr]) {
                         break;
                     }
                 }
 
                 if (!$display) {
                     $display = $user['displayname'] ?: $user['name'];
                 }
 
                 if ($display && $display != $folder_id) {
                     $display = "$display ($folder_id)";
                 }
 
                 return $display;
             }
 
             return $user;
         }
     }
 
     /**
      * Chwala's 'folder_mod' hook handler for mapping other users folder names
      */
     public static function folder_mod($args)
     {
         static $roots;
 
         if ($roots === null) {
             self::setup();
             $roots = self::$imap->get_namespace('other');
         }
 
         // Note: We're working with UTF7-IMAP encoding here
 
         if ($args['dir'] == 'in') {
             foreach ((array) $roots as $root) {
                 if (strpos($args['folder'], $root[0]) === 0) {
                     // remove root and explode folder
                     $delim  = $root[1];
                     $folder = explode($delim, substr($args['folder'], strlen($root[0])));
                     // compare first (user) part with a regexp, it's supposed
                     // to look like this: "Doe, Jane (uid)", so we can extract the uid
                     // and replace the folder with it
                     if (preg_match('~^[^/]+ \(([^)]+)\)$~', $folder[0], $m)) {
                         $folder[0] = $m[1];
                         $args['folder'] = $root[0] . implode($delim, $folder);
                     }
 
                     break;
                 }
             }
         }
         else { // dir == 'out'
             foreach ((array) $roots as $root) {
                 if (strpos($args['folder'], $root[0]) === 0) {
                     // remove root and explode folder
                     $delim  = $root[1];
                     $folder = explode($delim, substr($args['folder'], strlen($root[0])));
 
                     // Replace uid with "Doe, Jane (uid)"
                     if ($user = self::folder_id2user($folder[0], true)) {
                         $user      = str_replace($delim, '', $user);
                         $folder[0] = rcube_charset::convert($user, RCUBE_CHARSET, 'UTF7-IMAP');
 
                         $args['folder'] = $root[0] . implode($delim, $folder);
                     }
 
                     break;
                 }
             }
         }
 
         return $args;
     }
 }
diff --git a/plugins/libkolab/lib/kolab_utils.php b/plugins/libkolab/lib/kolab_utils.php
index 571bf286..d80d0140 100644
--- a/plugins/libkolab/lib/kolab_utils.php
+++ b/plugins/libkolab/lib/kolab_utils.php
@@ -1,93 +1,97 @@
 <?php
 
 /**
  * Utility class providing unified functionality for other plugins.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2012-2018, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_utils
 {
     public static function folder_form($form, $folder, $domain, $hidden_fields = array(), $no_acl = false)
     {
         $rcmail = rcmail::get_instance();
 
         // add folder ACL tab
         if (!$no_acl && is_string($folder) && strlen($folder)) {
             $form['sharing'] = array(
                 'name'    => rcube::Q($rcmail->gettext('libkolab.tabsharing')),
                 'content' => self::folder_acl_form($folder),
             );
         }
 
         $form_html = '';
 
         if (is_array($hidden_fields)) {
             foreach ($hidden_fields as $field) {
                 $hiddenfield = new html_hiddenfield($field);
                 $form_html .= $hiddenfield->show() . "\n";
             }
         }
 
         // create form output
         foreach ($form as $tab) {
-            if (is_array($tab['fields']) && empty($tab['content'])) {
+            if (isset($tab['fields']) && is_array($tab['fields']) && empty($tab['content'])) {
                 $table = new html_table(array('cols' => 2, 'class' => 'propform'));
                 foreach ($tab['fields'] as $col => $colprop) {
                     $label = !empty($colprop['label']) ? $colprop['label'] : $rcmail->gettext("$domain.$col");
 
                     $table->add('title', html::label($colprop['id'], rcube::Q($label)));
                     $table->add(null, $colprop['value']);
                 }
                 $content = $table->show();
             }
             else {
                 $content = $tab['content'];
             }
 
             if (!empty($content)) {
                 $form_html .= html::tag('fieldset', null, html::tag('legend', null, rcube::Q($tab['name'])) . $content) . "\n";
             }
         }
 
         return $form_html;
     }
 
     /**
      * Handler for ACL form template object
      */
     public static function folder_acl_form($folder)
     {
         $rcmail  = rcmail::get_instance();
         $storage = $rcmail->get_storage();
         $options = $storage->folder_info($folder);
 
         $rcmail->plugins->load_plugin('acl', true);
 
         // get sharing UI from acl plugin
         $acl = $rcmail->plugins->exec_hook('folder_form', array(
                 'form'    => array(),
                 'options' => $options,
                 'name'    => $folder
         ));
 
-        return $acl['form']['sharing']['content'] ?: html::div('hint', $rcmail->gettext('libkolab.aclnorights'));
+        if (!empty($acl['form']['sharing']['content'])) {
+            return $acl['form']['sharing']['content'];
+        }
+        
+        return html::div('hint', $rcmail->gettext('libkolab.aclnorights'));
     }
 }