Fatal error: Uncaught Error: Interface "Drupal\Core\Ajax\CommandInterface" not found in /home/www/drupal8/test/core/modules/ckeditor/src/Ajax/AddStyleSheetCommand.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/ckeditor/src/Ajax/AddStyleSheetCommand.php on line 10