Server Release 1.15.0 is Broken

[blink1073]

Description

File "/opt/hostedtoolcache/Python/3.10.2/x64/lib/python3.10/site-packages/jupyter_core/application.py", line 174, in load_config_file
    self.log.debug("Searching %s for config files", self.config_file_paths)

  File "/opt/hostedtoolcache/Python/3.10.2/x64/lib/python3.10/site-packages/jupyter_server/extension/application.py", line 168, in config_file_paths
    return self.serverapp.config_file_paths

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

Reproduce

Seen in https://github.com/jupyterlab/jupyterlab/runs/5536582051?check_suite_focus=true

Expected behavior

Context

Related to #715

[blink1073]

cc @minrk

[blink1073]

I'm reverting the PR for now to get downstreams working again.

[minrk]

Thanks for reverting. I thought from other unconditional access to self.serverapp.attr that ExtensionApps couldn't be used without a serverapp, but I guess that's not true? I'll make sure that case is handled and tested, but I don't really understand how it makes sense.

[blink1073]

Yeah, I'm not sure either, @Zsailer might have more insight.

[minrk]

I think #730 fixes it and includes a test