PHP Warning: preg_match() expects parameter 2 to be string, object given in /usr/share/kolab-syncroton/lib/kolab_sync_data_calendar.php on line 546
the parameter here can be indeed an object of type DateTime according to https://git.kolab.org/diffusion/RPK/browse/master/plugins/libkolab/lib/kolab_format_xcal.php;951f9f0efc740d8f75b512c90a6ae1a2fc187808$260.