Fatal error: Uncaught Error: Class "Symfony\Component\EventDispatcher\Event" not found in /home/www/drupal8/test/modules/migrate_plus/src/Event/MigratePrepareRowEvent.php:13 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/migrate_plus/src/Event/MigratePrepareRowEvent.php on line 13