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