I think this is a joke, possibly inspired by the XKCD comic (link posted in the stackoverflow comments). The string "Null" would not cause this behavior.
I have personally encountered "Null" as a surname in system used by job applicants world-wide. The system's session layer encodes absent values as the string "null" at some point. The Null clan is the only problematic case, and they are numerous enough that the maintainers are aware of the problem but not so numerous to fix the session layer.
I wish I could listen in on a dinner conversation at Null house. They must have an interesting perspective about computers.
It could very easily be real. I was in a Fantasy Football league on Yahoo a few years ago, and there was a player named Keith Null who played briefly after another player was injured. His name just showed up as Keith.