I remember @brettchalupa and I discussing this and sort of punting on it. In the light of a new day, I think I'd rather have a blank string as a smell than nil as a smell. Let's keep an eye on the hoops we find ourselves jumping through to handle users who've unlinked their Chef account: I could see that becoming a source of subtle repetition, which may lead us to a better long-term solution to this particular problem.

In the meantime, we can change this to return a blank string.