Fatal error: Uncaught Error: Interface "Sabre\Xml\XmlSerializable" not found in /home/tzuovhm/tzuovhm/apps_/dav/lib/CardDAV/Xml/Groups.php:13 Stack trace: #0 {main} thrown in /home/tzuovhm/tzuovhm/apps_/dav/lib/CardDAV/Xml/Groups.php on line 13