Fatal error: Uncaught Error: Class "Sabre\DAV\Collection" not found in /server/www/10.1.1.5/htdocs/vendor/sabre/dav/lib/CalDAV/Schedule/Outbox.php:22 Stack trace: #0 {main} thrown in /server/www/10.1.1.5/htdocs/vendor/sabre/dav/lib/CalDAV/Schedule/Outbox.php on line 22