@pimenas is correct. 
Specifics: Personally I am very much in favor of supporting both null, unrecognized, and case-insensitive matching in the enums. This is mostly because it ensures that if undocumented behavior changes, jclouds still works. (Clearly documented nullability might have to be handled differently, for example).

I actually like the logger.warn on UNRECOGNIZED and I think I will add it to the wiki example.