/**
  * Prepare the signature form with the default message.
  *
  * @param CRM_Campaign_Form_Petition_Signature $form
  *   The petition form.
  */
 public function buildSigForm($form)
 {
     $defaults = $form->getVar('_defaults');
     $messageField = $this->findMessageField();
     if ($messageField === FALSE) {
         return;
     }
     if (empty($this->petitionEmailVal[$this->fields['Default_Message']])) {
         return;
     } else {
         $defaultMessage = $this->petitionEmailVal[$this->fields['Default_Message']];
     }
     foreach ($form->_elements as $element) {
         if ($element->_attributes['name'] == $messageField) {
             $element->_value = $defaultMessage;
         }
     }
     $defaults[$messageField] = $form->_defaultValues[$messageField] = $defaultMessage;
     $form->setVar('_defaults', $defaults);
 }