public function merge(Ess_M2ePro_Model_Order_Item_Proxy $that)
{
$this->setQty($this->getQty() + $that->getOriginalQty());
$this->subtotal += $that->getOriginalPrice() * $that->getOriginalQty();
// merge additional data
// ---------------------------------------
$thisAdditionalData = $this->getAdditionalData();
$thatAdditionalData = $that->getAdditionalData();
$identifier = Ess_M2ePro_Helper_Data::CUSTOM_IDENTIFIER;
$thisAdditionalData[$identifier]['items'][] = $thatAdditionalData[$identifier]['items'][0];
$this->additionalData = $thisAdditionalData;
// ---------------------------------------
}
