Fatal error: Uncaught Error: Class "Drupal\Core\Render\Element\FormElement" not found in /home/www/drupal8/test/modules/webform/src/Element/WebformManagedFileBase.php:61 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Element/WebformManagedFileBase.php on line 61