anchor.diff:    bool anyItems;
   
     @Property(observer: 'itemsChanged')
  -  List<Todo> items = [];
  +  List<Todo> items;
   
     @Property(observer: 'storageIdChanged')
     String storageId = 'storage';
  
positive.code:   }
  
    @eventHandler
    int countActive() => items.where(filters['active']).length;
  
    @eventHandler
    int countCompleted() => items.where(filters['completed']).length;
  
    @eventHandler
    bool checkAllCompleted() {
  
negative.code: 
    @Observe('items.*')
    void itemsChanged() {
      if (storageId != null && items != null) {
        storage[storageId] = JSON.encode(items);
      }
    }
  