The `StepControl.advance` method now checks if the provided `model` or `data` Python objects are `None` before attempting to cast them to `MjModelWrapper` or `MjDataWrapper`, passing `nullptr` to the underlying C++ function if they are `None`.
This fixes an oversight in the python bindings, C++ code already supported null models.
PiperOrigin-RevId: 937243996
Change-Id: Ie67b8603517e7390fb54bfefbfed79ccf7b2bc5e
Matija Kecman
38956ed95c