Set to NULL for real in db values that equals NULL in PHP.
Without this change, events can not be edited on Postgres because it tries to set an invalid timestamp instead of NULL:
[28-Apr-2022 15:00:46 +0200]: <tv5na0nh> DB Error: [7] ERROR: invalid input syntax for type timestamp: ""
LINE 2: ...atus"='', "attendees"='', "alarms"='', "notifyat"='', "calda...
^ (SQL Query: UPDATE caldav_events
SET changed=now() , "start"='2022-04-29 16:00:00', "end"='2022-04-29 18:00:00', "all_day"='0', "recurrence_id"='0', "isexception"='0', "sequence"='0', "title"='test', "description"='', "location"='', "categories"='', "url"='', "free_busy"='1', "priority"='0', "sensitivity"='0', "status"='', "attendees"='', "alarms"='', "notifyat"='', "caldav_url"='/calendars/nicolas/default//D3F457A307C27F83D74BEE2AA8440C29-DEB97A759EE7B8BA.ics', "caldav_tag"=''
WHERE event_id='378'
AND calendar_id IN ('22','21')) in /usr/share/roundcube/program/lib/Roundcube/rcube_db.php on line 544 (POST /?_task=calendar&_action=event)
Set to NULL for real in db values that equals NULL in PHP. Without this change, events can not be edited on Postgres because it tries to set an invalid timestamp instead of NULL:
Only tested on PostgreSQL