3.x: Missing `NonNull` annotation on `Maybe<T>`

[KarboniteKream]

In #6840, the @NonNull annotation was added to various class generic types, including MaybeSource.
However, the annotation was omitted from Maybe itself. Was this intentional or was it just overlooked?

Apologies if this has been asked before, but I couldn't find any related issues/PRs.

[akarnokd]

Looks like a simple oversight. PR welcome.

[KarboniteKream]

Thanks for the clarification, let me submit it