You're likely testing a data field. It's actually by design in 2.1.x
It will be null until you start the recording (like on a real watch). You should be able to press the start button in the simulator window. And if you press the lap button, your DF can get the callback for a lap..
There's also a menu under the data filed line on the top where you can select a few different things about how the recording is occuring.