True, but I don't see how it is better. The test is specifically for None, which is the _selectedFilter_ keyword arg's default value (otherwise it should be a string). IMO, testing for None is semantically and logically correct for the way it is used here.

Any passed value for _selectedFilter_ that is not a string will result in a type error anyway during dialog construction (as with the noted issue, where QPyNullVariant was being passed).