Fatal error: Uncaught Error: Class "Drupal\Core\Form\ConfirmFormBase" not found in /home/www/drupal8/test/modules/webform/src/Form/WebformSubmissionDeleteMultiple.php:16
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/modules/webform/src/Form/WebformSubmissionDeleteMultiple.php on line 16