SerializedInventoryItemLocations.serialNumbers is always null

I'm trying to find a way to retrieve the serial numbers for a specific location for a specific item.  After browsing the schema browser and then doing some intellisense exploring I found what I thought was the correct way:

(this is just testing code in a "test bench" application)

 private void button5_Click(object sender, EventArgs e)  {      NSWSService service = NSWSService.Instance;        SerializedAssemblyItem item =           service.GetRecord<SerializedAssemblyItem>(null,               "520", RecordType.serializedAssemblyItem);        if (item != null)      {          foreach (SerializedInventoryItemLocations location in              item.locationsList.locations)          {              Console.WriteLine("Item 520, Location {0}",                   location.location);                if (String.IsNullOrEmpty(location.serialNumbers))              {                  continue;              }                string[] serialNumbers = location.serialNumbers.Split(                  new char[] { ',' });                foreach (string serialNumber in serialNumbers)              {                  Console.WriteLine("t{0}", serialNumber);              }          }      }  }