Does this means it's possible that we fail to unlock a locked file? if so, returning null should cause the audio error, and probably the player will stuck there and does nothing, but that's actually a potential bug in music app which we should but didn't handle before. I have mentioned this to Jim two days ago, and I think I will file a bug first then let's discuss how should we handle conditions like this. Also, we can keep the code here because it's not the bug of this patch.