Fatal error: Uncaught Error: Interface "TYPO3\CMS\Core\SingletonInterface" not found in /var/www/html/dev.hallescherfc.de/packages/muthsevcontent/Classes/Utility/PageTreeUtility.php:13 Stack trace: #0 {main} thrown in /var/www/html/dev.hallescherfc.de/packages/muthsevcontent/Classes/Utility/PageTreeUtility.php on line 13