In truth, if you don't do this, you'll just get a TypeError
exception. Now, you'll get an AssertionError.

Is this tangibly better? No.
Does mypy complain less? Yes.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200514055403.18902-21-jsnow@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>