The underlying issue was that the code was trying to directly assign a Python
dictionary to an add-on defined Group Property accessed via `[]` syntax, like
this:
```
to_bone['rigify_parameters'] = param_dict
```
That only works if 'rigify_parameters' does *not* already exist according to the
`[]` lookup, so this was failing whenever it already did.
This PR fixes that by simply deleting the property first when it already exists.
Co-authored-by: Ayoub ibn Muhammad <cl3m3c7@riseup.net>
Co-authored-by: Sybren A. Stüvel <sybren@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/135233
b634fd04ed