Code review comment for lp:~carla-sella/music-app/add_song_and_play

test_create_playlist_from_songs_tab fails with the following error on the Nexus 4:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/music_app/tests/test_music.py", line 465, in test_create_playlist_from_songs_tab
    self.assertThat(playlist, Not(Is(None)))
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 412, in assertThat
    raise MismatchError(matchee, matcher, mismatch, verbose)
MismatchError: None matches Is(None)