docs: update `useParams` hook return statement (#67384)
Hi 👋🏻
## The Change
I noticed that in one example of the [`useParams`
hook](https://nextjs.org/docs/app/api-reference/functions/use-params),
there is an old-fashioned return statement that returns a react fragment
instead of null. This step was part of the workaround from the
typescript environment from 2016, which is now obsolete.
Recently, I researched why some people do it today and whether we should
continue doing it in a react environment.
I created a document discussing it:
https://github.com/Kuboczoch/web-dev-best-practices/blob/master/react/conditional-rendering_return-react-fragment.md
tl;dr
> While returning a `React.Fragment` instead of `null` in a React
component was a workaround for TypeScript limitations in 2016, this is
no longer necessary. Returning `null` is more efficient, makes the code
more readable, is officially supported, and aligns with current best
practices.
## Why?
It helps to provide the best practice to other developers who are just
starting with web development and are mindlessly copy-pasting the code.
In this case, people do not need to research workarounds for TypeScript
from six years ago.
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Co-authored-by: Delba de Oliveira <32464864+delbaoliveira@users.noreply.github.com>
