Get to 100% branch coverage

Exercise edge cases in branch statements.
I wasn't aware. From my understanding [from][1] `ndb` (which may not be a perfect mapping), only one was to be used.

@proppy Do you happen to know if `id` and `name` can coexist?

[1]: https://code.google.com/p/appengine-ndb-experiment/source/browse/ndb/key.py?r=17ae1ecdc5b5bbbcd9379856970c511c4b13051a#466