Custom handlers in JupyterLab

Hello, I am trying to migrate from jupyter notebook to jupyter lab. I cannot find the right way to use a custom handler as described here: Custom handler documentation.

  1. When I hardcode the custom handler in the jupyter config file it doesn’t get read.
  2. When I pass it as an argument to the ‘jupyter lab’ command it breaks with:
    File “d:\program_files\anaconda3\envs\perper\lib\site-packages\traitlets\config\”, line 681, in load_config
    [2021-04-20T17:33:27.805Z] raise ArgumentError(“Invalid argument: ‘%s’”%raw)
    [2021-04-20T17:33:27.806Z] traitlets.config.loader.ArgumentError: Invalid argument: ‘–NotebookApp.nbserver_extensions’

I noticed that you didn’t mention the Jupyter Sever documentation, so I thought I should post it here: Documentation for Developers — Jupyter Server 1.7.0.dev0 documentation

Perhaps that could be implemented as an extension?