Page Not Found when deleting submission without destination parameter set

webform is trying to redirect to "node//results" when deleting submission with no destination parameter set.
The problem is $form_values['nid'] is empty, changing it to $form_values['node']->nid fixed the problem.

function webform_submission_delete_form_submit($form_id, $form_values) {
  webform_submission_delete($form_values['node'], $form_values['submission']);
  drupal_set_message(t("Submission deleted."));
  return 'node/'. $form_values['nid'] .'/results';
}