Well, that really seems to be the case, thanks for the heads up. Apparently, this has been discussed many times before, but I would expect something like this to be explicitly stated in the kata description, not left out in some vague discussion.

You might be throwing an instance of the Error class instead of the value provided as the parameter err. I had the same issue and that's how I got around it.

There's no way this is a 4 kyu problem, it's 6 at best. Besides, it doesn't even work in the first place. As stated before, it expects 1.2.3.4 to be invalid.