anchor.diff:    @override
     void visitChildren(AstVisitor visitor) {
       super.visitChildren(visitor);
  -    _safelyVisitChild(_returnType, visitor);
  -    _safelyVisitChild(_name, visitor);
  -    _safelyVisitChild(_functionExpression, visitor);
  +    _returnType?.accept(visitor);
  +    _name?.accept(visitor);
  +    _functionExpression?.accept(visitor);
     }
   }
   
  
positive.code: 
    @override
    void visitChildren(AstVisitor visitor) {
      _safelyVisitChild(_expression, visitor);
    }
  }
  
  
negative.code: 
    @override
    void visitChildren(AstVisitor visitor) {
      _expression?.accept(visitor);
    }
  }
  
  