tchan help me out about SerializedInventoryItem 's serialNumber.name

SerializedInventoryItemNumbersList siinl = new SerializedInventoryItemNumbersList();
SerializedInventoryItemNumbers[] siin; string siinName="";

searchPreferences.bodyFieldsOnly = false; //it's false now!!!

_service.search(item_inventory);

when I get (getlrres.recordList[i].GetType().Name == "SerializedInventoryItem")

then

siinl = sinventoryitem.numbersList;
if (siinl != null)
                            {
                                siin = siinl.numbers;
                                siinName = siin[0].serialNumber.name;
                            }


SerializedInventoryItem 's serialNumber.name   is  always null ,
only the internalId is not null.


why???  I need the serialNumber 's name!!! 
when the item get stock,I enter the serialNumber 's name  but I can't get it through suitetalk 's api....???