Fatal error: Uncaught Error: Interface "Drupal\Core\Field\FieldItemListInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Field/EntityReferenceFieldItemListInterface.php:8 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Field/EntityReferenceFieldItemListInterface.php on line 8