anchor.diff:  
       assertConstraint(
           [decoratedTypeAnnotation('int/*1*/').nullable],
  -        _mockOr(decoratedTypeAnnotation('int/*2*/').nullable,
  +        _either(decoratedTypeAnnotation('int/*2*/').nullable,
               checkExpression('(f())').nullCheck));
     }
   
  
positive.code: 
      assertConstraint(
          [decoratedTypeAnnotation('Int j').nullable],
          _mockOr(decoratedTypeAnnotation('Int other').nullable,
              checkExpression('j/*check*/').nullCheck));
    }
  
  
negative.code:     var nullable_j = decoratedTypeAnnotation('int j').nullable;
      var nullable_return = decoratedTypeAnnotation('int f').nullable;
      assertConstraint([nullable_i],
          _either(nullable_return, checkExpression('i/*check*/').nullCheck));
      assertConstraint([nullable_j],
          _either(nullable_return, checkExpression('j/*check*/').nullCheck));
    }
  
    test_if_without_else() async {
  