I don't think that Class::Null is really the Null design pattern, despite what it says. The pattern is for a stand-in collaborator who doesn't do anything, not something you add to a module to handle calls to undefined methods. Your module shouldn't ever have to know it is using a null object.
I'd agree but I hate arguing over terminology. If someone cares enough about design patterns to have an opinion on what pattern they're using, I'm unlikely care enough to correct them. (I'm not a big fan of the design patterns movement. Shoot me.)