Fatal error: Uncaught Error: Class "Drupal\Core\EventSubscriber\DefaultExceptionHtmlSubscriber" not found in /home/www/drupal8/test/modules/webform/src/EventSubscriber/WebformExceptionHtmlSubscriber.php:30 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/EventSubscriber/WebformExceptionHtmlSubscriber.php on line 30