Fatal error: Uncaught Error: Class "Drupal\Core\Entity\ContentEntityConfirmFormBase" not found in /home/www/drupal8/test/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php:14 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php on line 14