Fatal error: Uncaught Error: Class "SMW\Exporter\Serializer\Serializer" not found in /var/www/html/extensions/SemanticMediaWiki/src/Exporter/Serializer/RDFXMLSerializer.php:20 Stack trace: #0 {main} thrown in /var/www/html/extensions/SemanticMediaWiki/src/Exporter/Serializer/RDFXMLSerializer.php on line 20