anchor.diff:    TodoInput get _newTodo => $['new-todo'];
   
     @eventHandler
  -  bool itemsIsNotEmpty() => items.isNotEmpty;
  +  bool itemsIsNotEmpty() => items == null ? false : items.isNotEmpty;
   
     @eventHandler
     bool isZero(int value) => value == 0;
  
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);
      }
    }
  