[bug 933786] Fix test_null_device_returns_400
[bug 933786] Fix test_null_device_returns_400

This fixes the test so that it's testing the right thing and passes
correctly.

hoosteeno/fjord,rlr/fjord,lgp171188/fjord,rlr/fjord,mozilla/fjord,hoosteeno/fjord,lgp171188/fjord,staranjeet/fjord,DESHRAJ/fjord,lgp171188/fjord,rlr/fjord,staranjeet/fjord,rlr/fjord,mozilla/fjord,hoosteeno/fjord,Ritsyy/fjord,Ritsyy/fjord,staranjeet/fjord,hoosteeno/fjord,DESHRAJ/fjord,mozilla/fjord,lgp171188/fjord,staranjeet/fjord,Ritsyy/fjord,DESHRAJ/fjord,mozilla/fjord,Ritsyy/fjord