/**
  * Form builder callback.
  *
  * @todo I don't know why this needs to be separate from the form() method.
  * It was in the form_alter version but we should see if we can just fold
  * it into the method above.
  *
  * @param $entity_type
  * @param \Drupal\Core\Config\Entity\ConfigEntityInterface $bundle
  * @param array $form
  * @param \Drupal\Core\Form\FormStateInterface $form_state
  */
 public function formBuilderCallback($entity_type, ConfigEntityInterface $bundle, &$form, FormStateInterface $form_state)
 {
     // @todo write a test for this.
     $bundle->setThirdPartySetting('workbench_moderation', 'enabled', $form_state->getValue('enable_moderation_state'));
     $bundle->setThirdPartySetting('workbench_moderation', 'allowed_moderation_states', array_keys(array_filter($form_state->getValue('allowed_moderation_states'))));
     $bundle->setThirdPartySetting('workbench_moderation', 'default_moderation_state', $form_state->getValue('default_moderation_state'));
 }