Fatal error: Uncaught Error: Interface 'Sabre\Xml\XmlSerializable' not found in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/Xml/Property/SupportedCollationSet.php:22 Stack trace: #0 {main} thrown in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/Xml/Property/SupportedCollationSet.php on line 22