Can not start kernel with jupyterlab 4.0.0a31

[trungleduc]

Description

I'm using jupyterlab 4.0.0a31 with jupyter-server 2.0.0rc5, the notebook can not start the kernel with the following error message:

[E 2022-11-21 20:20:18.382 ServerApp] Uncaught exception GET /api/kernels/d355be5f-afdc-4809-acf7-f2a0c62ac0e4/channels?session_id=f7cf6c04-fceb-44b5-93f8-29f7eada37c6 (127.0.0.1)
    HTTPServerRequest(protocol='http', host='127.0.0.1:8888', method='GET', uri='/api/kernels/d355be5f-afdc-4809-acf7-f2a0c62ac0e4/channels?session_id=f7cf6c04-fceb-44b5-93f8-29f7eada37c6', version='HTTP/1.1', remote_ip='127.0.0.1')
    Traceback (most recent call last):
      File "/home/*****/mambaforge/envs/debug/lib/python3.9/site-packages/tornado/web.py", line 1713, in _execute
        result = await result
      File "/home/*****/mambaforge/envs/debug/lib/python3.9/site-packages/jupyter_server/services/kernels/websocket.py", line 62, in get
        await self.pre_get()
      File "/home/*****/mambaforge/envs/debug/lib/python3.9/site-packages/jupyter_server/services/kernels/websocket.py", line 58, in pre_get
        await self.connection.prepare()
      File "/home/*****/mambaforge/envs/debug/lib/python3.9/site-packages/jupyter_server/services/kernels/connection/channels.py", line 292, in prepare
        await self._register_session()
      File "/home/*****/mambaforge/envs/debug/lib/python3.9/site-packages/jupyter_server/services/kernels/connection/channels.py", line 284, in _register_session
        await stale_handler.close()
    TypeError: object NoneType can't be used in 'await' expression

Reproduce

1. Create a new environment with jupyterlab==4.0.0a31 and jupyter-server==2.0.0rc5
2. Open a notebook in JupyterLab

Expected behavior

Context

• Operating System and version: Ubuntu 22.04
• Browser and version: Chrome
• Jupyter Server version: 2.0.0rc5

[davidbrochart]

On my end, I get the following errors at JupyterLab startup:

[W 2022-11-21 22:23:31.281 ServerApp] jupyter_lsp | error adding extension (enabled: True): The module 'jupyter_lsp' could not be found (cannot import name 'WebSocketHandler' from 'jupyter_server.base.zmqhandlers' (/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_server/base/zmqhandlers.py)). Are you sure the extension is installed?
    Traceback (most recent call last):
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_server/extension/manager.py", line 175, in _validate_name
        self._module, self._metadata = get_metadata(name)
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_server/extension/utils.py", line 55, in get_metadata
        module = importlib.import_module(package_name)
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/importlib/__init__.py", line 126, in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
      File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
      File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
      File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
      File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
      File "<frozen importlib._bootstrap_external>", line 883, in exec_module
      File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_lsp/__init__.py", line 4, in <module>
        from .serverextension import load_jupyter_server_extension
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_lsp/serverextension.py", line 8, in <module>
        from .handlers import add_handlers
      File "/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_lsp/handlers.py", line 6, in <module>
        from jupyter_server.base.zmqhandlers import WebSocketHandler, WebSocketMixin
    ImportError: cannot import name 'WebSocketHandler' from 'jupyter_server.base.zmqhandlers' (/home/david/mambaforge/envs/tmp/lib/python3.10/site-packages/jupyter_server/base/zmqhandlers.py)

[davidbrochart]

I opened #1083.