/**
  * Order cancellation hook for payment method instance
  * Adds void transaction if needed
  * @return Mage_Sales_Model_Order_Payment
  */
 public function cancel()
 {
     if ($this->getMethodInstance()->getCode() == Braintree_Payments_Model_Creditcard::PAYMENT_METHOD_CODE) {
         Mage::register(self::REGISTRY_KEY_CANCEL, true);
     }
     return parent::cancel();
 }