I can't answer that yet. In fact, when I reported the issue I stated that I wasn't sure what the expected behavior should be (there's no requirement for it). I would think having a null value makes the most sense, but I'll update the thread when I hear.
This has been fixed, and the fix is available in the 1.1.1 SDK release, and it is available in the FR920XT 3.30 firmware release. The correct behavior is for the simulator and the device to both return null.