Run mypy without --no-strict-optional

[jpopelka]

1. remove --no-strict-optional from pre-commit-config
2. run pre-commit run --all-files
3. fix all errors

https://mypy.readthedocs.io/en/stable/kinds_of_types.html#no-strict-optional

See also packit/packit#1548 & packit/packit-service#1433

[stale]

This issue has been marked as stale because it hasn't seen any
activity for the last 60 days.

Stale issues are closed after 14 days, unless the label is removed
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Thank you for your contribution! 🦄 🚀 🤖

(Note: issues labeled with pinned or EPIC are
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[jpopelka]

See also #251

[stale]

This issue has been marked as stale because it hasn't seen any
activity for the last 60 days.

Stale issues are closed after 14 days, unless the label is removed
by a maintainer or someone comments on it.

This is done in order to ensure that open issues are still relevant.

Thank you for your contribution! 🦄 🚀 🤖

(Note: issues labeled with pinned or EPIC are
never marked as stale.)

[majamassarini]

Still relevant