Fatal error: Uncaught Error: Interface "TYPO3\CMS\Core\SingletonInterface" not found in /var/www/html/dev.hallescherfc.de/vendor/typo3/cms-dashboard/Classes/WidgetGroupRegistry.php:25 Stack trace: #0 {main} thrown in /var/www/html/dev.hallescherfc.de/vendor/typo3/cms-dashboard/Classes/WidgetGroupRegistry.php on line 25