Fatal error: Uncaught Error: Class 'Symfony\Component\EventDispatcher\Event' not found in /home/eberhardschwarze/public_html/vendor/contao/core-bundle/src/Event/PreviewUrlCreateEvent.php:20 Stack trace: #0 {main} thrown in /home/eberhardschwarze/public_html/vendor/contao/core-bundle/src/Event/PreviewUrlCreateEvent.php on line 20