CI pipeline fails for docs

Bug

Error description

Automatic docs creation during CI run fails since Oct 26th, while nothing related to doc created had been changed.

Error message

/builds/esde/machine-learning/mlair/docs/_source/customise.rst:181: WARNING: duplicate label how to access my customised model?, other instance in /builds/esde/machine-learning/mlair/docs/_source/autoapi/mlair/model_modules/model_class/index.rst
Exception occurred:
  File "/usr/lib/python3.6/site-packages/autoapi/extension.py", line 210, in doctree_read
    nodes[-1]["entries"].append((None, u"%s/index" % app.config.autoapi_root))
TypeError: 'generator' object is not subscriptable
The full traceback has been saved in /tmp/sphinx-err-aayhpu4e.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make: *** [Makefile:20: html] Error 2
cp: cannot stat './_build/html/*': No such file or directory
cp: cannot stat './_build/html/*': No such file or directory
failed

First guess on error origin

No real clue, have a look on local machine and try to reproduce error

Error origin

• error can be reprocuded when setup venv from scratch locally
• there is a pinned bug report on github related to an issue with sphinx and generator object

Solution

• reproduce error locally
• check error output at /tmp/ and search online for similar issues
• apply fix to pin docutils to <0.18 and check if this works