original.name="Fail_Invalid_3"
======
>>> main.whiley
type nat1 is (int x) where x >= 1
type neg is (int x) where x < 0

function f(int|null x) -> bool|null:
    //
    if x is nat1:
        return true
    else if x is null:
        return false
    else:
        fail

public export method test():
    assume f(1) == true
    assume f(null) == false
    assume f(-1) == null
---
E712 main.whiley 11,8:11
E729 main.whiley 11,8:11