mutmut results fails with "AttributeError: 'NoneType' object has no attribute 'paths_to_mutate'"

[WillGibson]

I am working to compare mutmut and Cosmic Ray before deciding which one to stick with for mutation testing on our codebase.

Draft pull request where I am working: https://github.com/uktrade/platform-tools/pull/648.

You can see the error in this GitHub Action: https://github.com/uktrade/platform-tools/actions/runs/11930476073/job/33251331130

Steps to replicate locally...

git clone git@github.com:uktrade/platform-tools.git
git checkout ad66d4f
# I'm not sure if we should have run mutmut before we try to get results, the behaviour is the same either way.
poetry run mutmut run || exit 1 # Explained in https://github.com/boxed/mutmut/issues/346
poetry run mutmut run
poetry run mutmut results # Watch it fail

[boxed]

Fixed in 3.2.2

[WillGibson]

I can confirm this after updating. Thanks @boxed.