Fatal error: Uncaught Error: Class 'HTMLPurifier_ChildDef_Required' not found in /opt/lampp/htdocs/io.core.websocket/vendor/ezyang/htmlpurifier/library/HTMLPurifier/ChildDef/Optional.php:10 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/io.core.websocket/vendor/ezyang/htmlpurifier/library/HTMLPurifier/ChildDef/Optional.php on line 10