I'm a little confused here, but it doesn't have anything to do with your change -- it's because of the existing code. So, we get a string by evaluating `block_payload['edit_info']['previous_version']`, and then we check if that string exists as a key in the `result` dict, and if that key isn't present, then we set it with a value of `set()`. There's a lot of logic going on there, but I can follow it.

But then the `setdefault()` call apparently returns the set, and we add something else to it? Does that update it in the `results` dict? What happens if the key didn't exist -- do we return the same set that was added to the dict, or a new set? This line of code is doing a *lot*, and it's hard to follow.