Since C# 8.0 we have not only nullable value types (e.g. `int?` or `Nullable<int>`), but nullable reference types as well (e.g. `string?`). This means it's possible to have a maybe monad that does not require an extra generic type like `Maybe<T>`. Instead we can implement the monad purely via extension methods on `T?`.
Due to the C#'s awkward dichotomy between value and reference types this involves some busy work, so I created a small package for interested parties.