Fix typing error due to Optional

[Atry]

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Optional is not a valid type because it needs type parameter

What does this PR do?

Fix typing error due to Optional

Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [x] Did you read the contributor guideline, Pull Request section?
• [ ] Was this discussed/approved via a Github issue or the forum? Please add a link to it if that's the case.
• [ ] Did you make sure to update the documentation with your changes? Here are the documentation guidelines, and here are tips on formatting docstrings.
• [ ] Did you write any new necessary tests?

Who can review?

@OlivierDehaene OR @Narsil

[OlivierDehaene]

Where are these errors coming from? Is it your ide flagging it? Or mypy? In my opinion it correctly hints at what past key values is

[Atry]

Oh, I am using Pylance, which seems stricter than mypy

[Atry]

The error message is

Expected one type argument after "Optional"