AttributeError: 'NoneType' object has no attribute 'reraise_server_extension_failures'

[Carreau]

$ jupyter server extension enable

(something something syntax error unrelated in my extension)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/bin/jupyter-server", line 8, in <module>
    sys.exit(main())
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_core/application.py", line 264, in launch_instance
    return super(JupyterApp, cls).launch_instance(argv=argv, **kwargs)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/config/application.py", line 846, in launch_instance
    app.start()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/serverapp.py", line 2667, in start
    self.start_app()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/serverapp.py", line 2565, in start_app
    super(ServerApp, self).start()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_core/application.py", line 253, in start
    self.subapp.start()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/serverextension.py", line 372, in start
    super(ServerExtensionApp, self).start()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_core/application.py", line 253, in start
    self.subapp.start()
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/serverextension.py", line 275, in start
    self.toggle_server_extension(arg)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/serverextension.py", line 244, in toggle_server_extension
    config_dir, extension_manager = _get_extmanager_for_context(
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/serverextension.py", line 63, in _get_extmanager_for_context
    extension_manager = ExtensionManager(
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/config/configurable.py", line 85, in __init__
    super(Configurable, self).__init__(**kwargs)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/traitlets.py", line 1082, in __init__
    super_kwargs[key] = value
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/contextlib.py", line 124, in __exit__
    next(self.gen)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/traitlets.py", line 1216, in hold_trait_notifications
    self.notify_change(change)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/traitlets.py", line 1229, in notify_change
    return self._notify_observers(change)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/traitlets/traitlets.py", line 1266, in _notify_observers
    c(event)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/manager.py", line 260, in _config_manager_changed
    self._load_config_manager(change.new)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/manager.py", line 315, in _load_config_manager
    self.from_jpserver_extensions(jpserver_extensions)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/manager.py", line 320, in from_jpserver_extensions
    self.add_extension(name, enabled=enabled)
  File "/Users/bussonniermatthias/miniforge3/envs/papyri/lib/python3.9/site-packages/jupyter_server/extension/manager.py", line 332, in add_extension
    if self.serverapp.reraise_server_extension_failures:
AttributeError: 'NoneType' object has no attribute 'reraise_server_extension_failures'

It's not critical as it ends up reraising indirectly because of the Attribute error, but filling it anyway.
(self.serverapp is an Any(), trait).