Fatal error: Uncaught Error: Class "Drupal\Core\Queue\QueueWorkerBase" not found in /home/www/drupal8/test/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php:19 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php on line 19