I've seen a bunch of code like this, usually written by juniors once they get a bit of experience and discover the concept of types. A surefire way to make your Python code terrible. The whole point of Python is the duck typing. If you're not going to use that then you might as well use a real programming language.
Code, like the one provided by the OP, should be valued and encouraged to prevent future bugs. Incorporating tools like Mypy during pre-commit and pyright during code editing can make a significant difference. This approach helps eliminate the need for writing unnecessary unit tests that check for None type.
In my opinion, as a mid-senior developer, I always appreciate the use of types in Python. If you are confident about having predictable inputs, you can rely on duck typing and use it primarily for scripting purposes.