anchor.diff:  
     @override
     void visitChildren(AstVisitor visitor) {
  -    _safelyVisitChild(_target, visitor);
  -    _safelyVisitChild(_methodName, visitor);
  -    _safelyVisitChild(_typeArguments, visitor);
  -    _safelyVisitChild(_argumentList, visitor);
  +    _target?.accept(visitor);
  +    _methodName?.accept(visitor);
  +    _typeArguments?.accept(visitor);
  +    _argumentList?.accept(visitor);
     }
   }
   
  
positive.code: 
    @override
    void visitChildren(AstVisitor visitor) {
      _safelyVisitChild(_block, visitor);
    }
  }
  
  
negative.code:   @override
    void visitChildren(AstVisitor visitor) {
      super.visitChildren(visitor);
      _name?.accept(visitor);
      _typeParameters?.accept(visitor);
      _superclass?.accept(visitor);
      _withClause?.accept(visitor);
      _implementsClause?.accept(visitor);
    }
  }
  
  