AttributeError: module 'sphinx_csharp.csharp' has no attribute 'CSharpNamespacePlain'

[red8888]

I get the following error when adding the sphinx_csharp extension

Exception occurred:
  File "/usr/local/lib/python3.9/site-packages/breathe/renderer/sphinxrenderer.py", line 185, in <module>
    class CSharpNamespacePlain(BaseObject, cs.CSharpNamespacePlain):
AttributeError: module 'sphinx_csharp.csharp' has no attribute 'CSharpNamespacePlain'
The full traceback has been saved in /var/folders/gj/_wrr7xy53f5bkr53zt2zp4qw0000gp/T/sphinx-err-gl7u19db.log, if you want to report the issue to the developers.

[rogerbarton]

You should use my fork, which is much more up to date. The breathe integration only works with my fork. Also im not sure if python 3.9 is supported.