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I just see your branch is out of date with master, I guess a rebase will do the trick.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