that's something I'm doing all the time: not trying to test the "correct" value of a variable, but at least every incorrect value possible (None, 0, "", False, etc).
Of course, this is not 100% proof, because if the "year" provided is a string, the condition is False and the rest of the method goes bananas.

Anyway, for the general purposes, testing "not year" and "year is None" will lead to the same result.