Roundcube 1.2.3 + libcalendaring, kolab/calendar, kolab/tasklist (all from git 27.12.2016) using MySQL driver

1. Create new task with no status (default ---)
2. Click on this task in the list and choose "Edit"
3. Click Save.
4. "Failed to save data" message is displayed

Roundcube error log:

[01-Jan-2017 08:24:33 +0100]: <vnun16dl> DB Error: [1048] Column 'status' cannot be null (SQL Query: UPDATE tasks

SET   changed=now() , `title`='test5', `description`='', `flagged`='0', `complete`='0.00', `parent_id`=NULL, `date`=NULL, `time`=NULL, `startdate`=NULL, `starttime`=NULL, `alarms`=NULL, `recurrence`=NULL, `status`=NULL, `tags`='', `notify`=NULL
WHERE task_id='8'
AND   tasklist_id IN ('2')) in /pathtoroundcube/program/lib/Roundcube/rcube_db.php on line 539 (POST /?_task=tasks&_action=task)

So it seems that this edit script interprets default no status value ('') as NULL and then fails due to NOT NULL constrain on this column