id: ts-defensive-null-guard
valid:
  - |
    function f(x) { if (x === null) return null; }
  - |
    function f(x) {
      if (x === null) return null;
      if (x === undefined) return null;
    }
invalid:
  - |
    function f(x) { if (x === null || x === undefined) { return null; } }
  - |
    function f(x) { if (x == null) { return null; } }