interesting situation which is probably a weird edge case -- my index only has one document. I asekd it a stupid question ("how do I do it?") and it returned that one document. It's not REALLY relevant, but I suppose it's not entirely irrelevant either. Is it a guarantee that with only one indexed document, you'll always get it? I used "chicken?" as the query and it still retrieved that document -- there is nothing to do with even animals in it.
By default you should be returning the most similar document, if there is one document that will be the most similar one. You can implement a similarity cutoff in these scenarios to ensure they're at least somewhat relevant