/**
  * fillout the shipping price group payload for the order item
  * @param  Mage_Sales_Model_Order_Address
  * @param  IOrderItem
  * @return self
  */
 protected function prepareShippingPriceGroup(Mage_Sales_Model_Order_Address $address, IOrderItem $payload)
 {
     $shippingPriceGroup = $payload->getEmptyPriceGroup();
     $shippingPriceGroup->setAmount((double) $address->getShippingAmount());
     $this->discountHelper->transferDiscounts($address, $shippingPriceGroup);
     $payload->setShippingPricing($shippingPriceGroup);
     return $this;
 }