Cannot override settings by `null` value

[aidy1991]

Description

Our application uses jupyterlab's settings override feature to change the settings of some extensions.
However, due to an upgrade of jupyterlab_server (v2.5.2 => v2.12.0), the settings are no longer overridden.
From my investigation, settings are not overridden if the value is null, as in { "format": null }. This is probably because recursive_update used in the following location ignores properties with the value None.

jupyterlab_server/jupyterlab_server/settings_utils.py

Line 297 in d5c07d6

recursive_update(overrides.setdefault(plugin_id, {}), config)

Reproduce

I faced this problem when overriding the jupyter-archive configuration. Therefore, below I describe how to reproduce the problem in the case of jupyter-archive. However, the same should be true for other settings as well.

1. Install jupyter-archive extension
2. Check the default setting of format is zip on Advanced Settings Editor
3. Add sys.prefix>/local/share/jupyter/lab/settings/overrides.json and see below for the contents of this file
4. Check that the default setting of format is not overridden
   (5. If you set non-null value like tgz, it works well)

Expected behavior

In previous versions of jupyterlab_server, setting values could be overridden with null. Newer versions should be able to do the same, I think.

Context

• JupyterLab version: 3.0.16
• jupyterlab_server that worked well: 2.5.2
• jupyterlab_server that does not work well: 2.12.0

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[blink1073]

Hi @aidy1991, would you open to submitting a PR to jupyter_server to add handling of None in recursive_update?

[aidy1991]

Hi blink1073, thank you for your reply!

jupyter_server's recursive_update() is already handling None.
Removing key from target when value is None is a specification of recursive_update() and has been so for 5 years.
https://github.com/jupyter-server/jupyter_server/blob/3e64fa5eef7fba9f8e17c30cec688254adf913bd/jupyter_server/config_manager.py#L28-L30

On the other hand, jupyterlab_server changed its usage of recursive_update() 6 months ago.
Therefore, I think we need to address this issue on the jupyterlab_server side.
e0fc91b#diff-9af31a1313a162bb540c3ae2c11a74ee859d433f83814c0769c8a1d4ce0e4405R302

[blink1073]

Ah, I see. A PR here would be welcome then. 😄