Fatal error: Uncaught Error: Class "Symfony\Component\EventDispatcher\Event" not found in /home/www/drupal8/test/core/modules/migrate/src/Event/MigrateMapSaveEvent.php:11 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate/src/Event/MigrateMapSaveEvent.php on line 11