I think your post only takes non-null values into account, which is what OP seems to talk about. What would this code do? Optional<Int> foo = null; foo

I think your post only takes non-null values into account, which is what OP seems to talk about. What would this code do? Optional<Int> foo = null; foo.flatMap(x -> Optional.of(x)); Obeying the Monad laws would mean getting null as a result, via `m.flatMap(x -> Optional.of(x)) = m` for all m (or `m >>= pure = m` if you prefer Haskell syntax).