Failing gracefully for inconsistent APIs

I‘m using Mantle for model objects representing the objects of the Reddit API (https://github.com/reddit/reddit/wiki/JSON) and unfortunately the API behaves pretty inconsistent. Replies on a comment expect a dictionary (which I usually get), but when there are no replies the value sometimes is an empty string instead of nil.

I'm opening this Pull Request to start a discussion on how to handle such cases, I'm sure there are more problematic APIs out there - I don't know if you would want to include this kind of fallback/hack in Mantle though. Is the changed code reasonable for my use case or am I missing a better fix?