anchor.diff:    @override
     void visitChildren(AstVisitor visitor) {
       super.visitChildren(visitor);
  -    _safelyVisitChild(_name, visitor);
  +    _name?.accept(visitor);
       _constants.accept(visitor);
     }
   }
  
positive.code:   @override
    void visitChildren(AstVisitor visitor) {
      super.visitChildren(visitor);
      _safelyVisitChild(_name, visitor);
      _safelyVisitChild(_bound, visitor);
    }
  }
  
  
negative.code: 
    @override
    void visitChildren(AstVisitor visitor) {
      _name?.accept(visitor);
      _value?.accept(visitor);
      _libraryUri?.accept(visitor);
    }
  }
  
  