Fatal error: Uncaught Error: Class "Drupal\migrate\Event\EventBase" not found in /home/www/drupal8/test/core/modules/migrate/src/Event/MigrateImportEvent.php:8 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/migrate/src/Event/MigrateImportEvent.php on line 8