diff --git a/plugins/kolab_addressbook/kolab_addressbook.php b/plugins/kolab_addressbook/kolab_addressbook.php
--- a/plugins/kolab_addressbook/kolab_addressbook.php
+++ b/plugins/kolab_addressbook/kolab_addressbook.php
@@ -227,36 +227,38 @@
     public function folder_tree_html($node, $data, &$jsdata)
     {
         $out = '';
-        foreach ($node->children as $folder) {
-            $id = $folder->id;
-            $source = $data[$id];
-            $is_collapsed = strpos($this->rc->config->get('collapsed_abooks',''), '&'.rawurlencode($id).'&') !== false;
-
-            if ($folder->virtual) {
-                $source = $this->abook_prop($folder->id, $folder);
-            }
-            else if (empty($source)) {
-                $this->sources[$id] = new rcube_kolab_contacts($folder->name);
-                $source = $this->abook_prop($id, $this->sources[$id]);
-            }
+        if (!empty($node->children)) {
+            foreach ($node->children as $folder) {
+                $id = $folder->id;
+                $source = $data[$id];
+                $is_collapsed = strpos($this->rc->config->get('collapsed_abooks',''), '&'.rawurlencode($id).'&') !== false;
+
+                if ($folder->virtual) {
+                    $source = $this->abook_prop($folder->id, $folder);
+                }
+                else if (empty($source)) {
+                    $this->sources[$id] = new rcube_kolab_contacts($folder->name);
+                    $source = $this->abook_prop($id, $this->sources[$id]);
+                }
 
-            $content = $this->addressbook_list_item($id, $source, $jsdata);
+                $content = $this->addressbook_list_item($id, $source, $jsdata);
 
-            if (!empty($folder->children)) {
-                $child_html = $this->folder_tree_html($folder, $data, $jsdata);
+                if (!empty($folder->children)) {
+                    $child_html = $this->folder_tree_html($folder, $data, $jsdata);

-                // copy group items...
-                if (preg_match('!<ul[^>]*>(.*)</ul>\n*$!Ums', $content, $m)) {
-                    $child_html = $m[1] . $child_html;
-                    $content = substr($content, 0, -strlen($m[0]) - 1);
-                }
-                // ... and re-create the subtree
-                if (!empty($child_html)) {
-                    $content .= html::tag('ul', array('class' => 'groups', 'style' => ($is_collapsed ? "display:none;" : null)), $child_html);
+                    // copy group items...
+                    if (preg_match('!<ul[^>]*>(.*)</ul>\n*$!Ums', $content, $m)) {
+                        $child_html = $m[1] . $child_html;
+                        $content = substr($content, 0, -strlen($m[0]) - 1);
+                    }
+                    // ... and re-create the subtree
+                    if (!empty($child_html)) {
+                        $content .= html::tag('ul', array('class' => 'groups', 'style' => ($is_collapsed ? "display:none;" : null)), $child_html);
+                    }
                 }
-            }
 
-            $out .= $content . '</li>';
+                $out .= $content . '</li>';
+            }
         }
 
         return $out;