error after adding c.NotebookApp.contents_manager_class = 'notedown.NotedownContentsManager'

[carter54]

In order to read md file directly in Jupyter Notebook, I install notedown.

But after adding c.NotebookApp.contents_manager_class = 'notedown.NotedownContentsManager' at the end of my config file 'jupyter_notebook_config.py'
or
using jupyter notebook --NotebookApp.contents_manager_class='notedown.NotedownContentsManager'

I get the following error:

Bad config encountered during initialization: The 'contents_manager_class' trait of a NotebookApp instance must be a subclass of 'notebook.services.contents.manager.ContentsManager', but a value of class 'traitlets.traitlets.MetaHasTraits' (i.e. <class 'notedown.contentsmanager.NotedownContentsManager'>) was specified.

Any idea what cause this error? When I delete jupyter notebook --NotebookApp.contents_manager_class='notedown.NotedownContentsManager' the notebook works fine.

[Apollo2Mars]

I have the same problem, do you solve this problem?

[zbisure]

jupyter 1.0.0
jupyter-client 6.2.0
jupyter-core 4.7.1
jupyter_console 5.2.0
jupyterlab-pygments 0.1.2
jupyterlab-widgets 1.0.0
notebook 6.4.0
notedown 1.5.1
You can try the above configuration