dhall-1.4.2: Prelude/Optional/null

{-
Returns `True` if the `Optional` value is absent and `False` if present

Examples:

```
./null Integer ([2] : Optional Integer) = False

./null Integer ([] : Optional Integer) = True
```
-}
let null : ∀(a : Type) → Optional a → Bool
    =   λ(a : Type)
    →   λ(xs : Optional a)
    →   Optional/fold a xs Bool (λ(_ : a) → False) True

in  null