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