It'd be great to expand this line to improve clarity. Also, this returns nil if a nil hub is passed and default is set to false, is that expected and ok?

@brandonarbini and I both took a pass at rewriting it at
https://gist.github.com/brandonarbini/4fb2b35a9c0895fe49ad and https://gist.github.com/chriswarren/81e5a43c2505fd8c605f.

We think the second one is the way to go, assuming that a nil check on hub produces the same result as checking `get_hub_config(nil, API_BASE_URL_KEY)`, but it'd be great to hear your thoughts on it.