# Description

This MR initializes `self._body_physx_view = None` in the init method of the
`ContactSensor` class.

This is needed to use ContactSensors with `debug_vis=True` while running
Orbit as an extension, such as EvalSim.

Currently, `ContactSensor._initialize_impl` initializes and sets the
value of `self._body_physx_view`. However, when running in extension
mode, `ContactSensor._initialize_impl` is called _after_
`ContactSensor._debug_vis_callback`, which causes an error to appear
upon loading an environment because `ContactSensor._debug_vis_callback`
references `self._body_physx_view` that have not been initialized.

With `self._body_physx_vew` initialized to None in the init method of
`ContactSensor`, it allows `ContactSensor._debug_vis_callback` to be
safely called before `ContactSensor._initialize_impl`.

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] I have run all the tests with `./orbit.sh --test` and they pass
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there