/**
  * This function returns a form that allows a user
  * to change the modifier to the order.
  *
  * We have mainly added this function as an example!
  *
  * @param Controller $optionalController  - optional custom controller class
  * @param Validator $optionalValidator  - optional custom validator class
  * @return OrderModifierForm or subclass
  */
 public function getModifierForm(Controller $optionalController = null, Validator $optionalValidator = null)
 {
     if ($this->ShowForm()) {
         $fields = new FieldList();
         $fields->push($this->headingField());
         $fields->push($this->descriptionField());
         return OrderModifierForm::create($optionalController, "ModifierForm", $fields, $actions = new FieldList(), $optionalValidator);
     }
 }