Fatal error: Uncaught Error: Class 'Sabre\DAVACL\AbstractPrincipalCollection' not found in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/CalendarRoot.php:20 Stack trace: #0 {main} thrown in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/CalendarRoot.php on line 20