Well, they do correspond to the "Maybe a" for some fixed type a, and Maybe is a monad, however you are right that it would be clearer to to say Maybe or Nullabl

Well, they do correspond to the "Maybe a" for some fixed type a, and Maybe is a monad, however you are right that it would be clearer to to say Maybe or Nullable or Option type, since that's what is meant, not some general monad.