Raise exception in `add_year`

[gidden]

Required: write a single sentence that describes the changes made by this PR.

This PR raises an exception at the start of add_year()

How to review

Required: describe specific things that reviewer(s) must do, in order to ensure that the PR achieves its goal. If no review is required, write “No review:” and describe why.

Confirm that tests still pass and advise on any issues that arise as a result of non-passage

PR checklist

• [ ] Continuous integration checks all ✅

• [ ] Add or expand tests; coverage checks both ✅
• [ ] Add, expand, or update documentation.
• [ ] Update release notes.

[gidden]

Please advise on whether to run black here which results in a large diff

[LauWien]

Please advise on whether to run black here which results in a large diff

~Hm, possible we can create a new PR where we run black in the whole repository and then rebase this PR once merged? @khaeru what do you think?~

[LauWien]

Please advise on whether to run black here which results in a large diff

I just see your branch is out of date with master, I guess a rebase will do the trick.

[gidden]

ah hah - let me rebase and cherry-pick