[Bug]: useParams type has changed from `string` to `string | undefined`

[tim-field]

What version of React Router are you using?

v6

Steps to Reproduce

If I have a route /:id

Expected Behavior

Its not possible for the component assigned to render with id as undefined

Actual Behavior

But since this PR was merged, id is typed as string | undefined

#8019 (comment)

This is breaking a fair few things for us, and AFAIK its not possible to have optional parameters in V6 so the undefined type here isn't correct ?

[timdorr]

v6 is still in beta, so breaking changes are still acceptable.

Regardless, there's no way for the type system to know at compile time (not run time) that the provided URL must include that parameter. Hence, to avoid bugs from the type system lying to you, it should be marked as Optional.