Fatal error: Uncaught Error: Class "Drupal\Core\Ajax\AjaxResponse" not found in /home/www/drupal8/test/modules/webform/src/Ajax/WebformSubmissionAjaxResponse.php:15 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Ajax/WebformSubmissionAjaxResponse.php on line 15