Fatal error: Uncaught Error: Class "Drupal\field_ui\Form\EntityDisplayModeFormBase" not found in /home/www/drupal8/test/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php:13
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php on line 13