/**
  * {@inheritdoc}
  */
 public function form(array $form, FormStateInterface $form_state)
 {
     // Hide subscription widget if only one newsletter available.
     if (count($this->getNewsletters()) == 1) {
         $this->getSubscriptionWidget($form_state)->setHidden();
     }
     $form = parent::form($form, $form_state);
     $form['message'] = array('#type' => 'item', '#markup' => $this->message);
     return $form;
 }