> I think the round() function should explicitly check for None and replace it with zero

That would be a change in behaviour: `round(x)` is not the same as `round(x, 0)`. For most types, `round(x)` returns an `int`, while `round(x, 0)` returns something of the same type as `x`. Instead, I think we should add the check for `None` to `int`s `__round__` implementation.

>>> round(1.3, 0)
1.0
>>> round(1.3)
1
>>> round(1.3, None)
1