Docs build error in Sphinx 4.0.0

[akihironitta]

🐛 Bug

I locally confirmed that building docs (cd docs; make html) fails due to:

Extension error (sphinx_paramlinks.sphinx_paramlinks):
Handler <function build_index at 0x7f20c201c820> for event 'doctree-read' threw an exception (exception: __new__() missing 1 required positional argument: 'aliased')
make: *** [Makefile:19: html] Error 2
Traceback (most recent call last):
  File "/entrypoint.py", line 22, in <module>
    action.build_all_docs(github_env, [os.environ.get("INPUT_DOCS-FOLDER")])
  File "/sphinx_action/action.py", line 167, in build_all_docs
    raise RuntimeError("Build failed")
RuntimeError: Build failed

and also confirmed that pip install Sphinx<4.0.0 fixes the error.

To Reproduce

https://github.com/PyTorchLightning/pytorch-lightning/pull/7452/checks?check_run_id=2538915517

Expected behavior

make html should successfully build the docs.

[astrojuanlu]

I didn't see a corresponding issue upstream, so I opened one sqlalchemyorg/sphinx-paramlinks#9