Fatal error: Uncaught Error: Class "Drupal\field_ui\Form\EntityDisplayModeFormBase" not found in /home/www/drupal8/test/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php on line 10