Language server warnings

Description

After installing the 3.8 version along with jupyter-lsp 1.4.0, new server warnings are logged when running jupyterlab in the format:

Failed to validate commands from language server spec finder `x-language-server`: [<ValidationError: "None is not of type 'string'">]

for some of the language server specs defined here (See list below) Command Line Output:

[W 2021-07-06 12:28:01.705 ServerApp] Failed to validate commands from language server spec finder `bash-language-server`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.705 ServerApp] Failed to validate commands from language server spec finder `dockerfile-language-server-nodejs`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.706 ServerApp] Failed to validate commands from language server spec finder `javascript-typescript-langserver`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.708 ServerApp] Failed to validate commands from language server spec finder `pyright`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.710 ServerApp] Failed to validate commands from language server spec finder `sql-language-server`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.712 ServerApp] Failed to validate commands from language server spec finder `unified-language-server`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.712 ServerApp] Failed to validate commands from language server spec finder `vscode-css-languageserver-bin`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.713 ServerApp] Failed to validate commands from language server spec finder `vscode-html-languageserver-bin`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.713 ServerApp] Failed to validate commands from language server spec finder `vscode-json-languageserver-bin`:
    [<ValidationError: "None is not of type 'string'">]
[W 2021-07-06 12:28:01.714 ServerApp] Failed to validate commands from language server spec finder `yaml-language-server`:
    [<ValidationError: "None is not of type 'string'">]

I believe this is be related to troubleshooting introduced in #634 where a new property is added to the schema but some of the server language specs are not including it.

Reproduce

1. Install jupyterlab (3.0.14)
2. Install jupyterlab-lsp (3.8.0) and jupyter-lsp (1.4.0)
3. Run jupyter lab with the --debug flag and watch for warning logs

Expected behavior

Either no warnings logged for missing servers, or a way to turn them off?

Context

• Operating System and version: MacOS Version 11.3.1
• Browser and version: Chrome Version 91.0.4472.114
• JupyterLab version: 3.0.14

Required: installed server extensions

    jupyter_lsp enabled
    - Validating jupyter_lsp...
      jupyter_lsp 1.4.0 OK
    jupyterlab enabled
    - Validating jupyterlab...
      jupyterlab 3.0.14 OK
    nbclassic enabled
    - Validating nbclassic...
      nbclassic  OK

Required: installed lab extensions

JupyterLab v3.0.14
my-conda-env/share/jupyter/labextensions
        bqplot v0.5.26 enabled OK (python, bqplot)
        @krassowski/jupyterlab-lsp v3.8.0 enabled OK (python, jupyterlab-lsp)
        @jupyter-widgets/jupyterlab-manager v3.0.0 enabled OK (python, jupyterlab_widgets)
Other labextensions (built into JupyterLab)
app dir: my-conda-env/share/jupyter/lab

[karlaspuldaro]

I can help looking into this

[krassowski]

Thank you. We need to improve the validator output as it is hard to tell what failed from these logs, but I believe your assessment right. An immediate solution is could be to update the schema to accept null for troubleshoot. I agree that ideally we would not be showing warnings for servers which are not installed.