> Option types are way better and always do what you expect.

No, I can implement the exact same weird functions with option types, with signatures

sum: Array<Int> -> Optional<Int>

count_elements: Array<Int> -> Int

FWIW, I personally prefer both functions to not return Optionals, but the point is that the mere presence of Option types in your type system (and the absence of null pointers) doesn't magically eliminate bad library design