Fatal error: Uncaught Error: Class 'Sabre\DAV\Locks\Backend\AbstractBackend' not found in /home/malert/WebDAV/vendor/sabre/dav/lib/DAV/Locks/Backend/File.php:20 Stack trace: #0 {main} thrown in /home/malert/WebDAV/vendor/sabre/dav/lib/DAV/Locks/Backend/File.php on line 20