anchor.diff:    KeyValueChangeRecord _additionsTail;
   
     KeyValueChangeRecord _removalsHead;
  -
  -  // ignore: unused_field
  -  KeyValueChangeRecord _removalsTail;
   
     bool get isDirty {
       return !identical(this._additionsHead, null) ||
  
positive.code:       }
      });
  
      // Items remaining at the end of the list have been removed.
      if (insertBefore != null) {
        // Truncate end of list.
        insertBefore._prev?._next = null;
  
        _removalsHead = insertBefore;
        _removalsTail = insertBefore;
  
        if (_removalsHead == _mapHead) {
          _mapHead = null;
        }
  
        for (var record = insertBefore;
            record != null;
            record = record._nextRemoved) {
          _records.remove(record.key);
          record._nextRemoved = record._next;
          record.previousValue = record.currentValue;
          record.currentValue = null;
          record._prev = null;
          record._next = null;
        }
      }
  
  
negative.code:     KeyValueChangeRecord record;
      for (record = this._removalsHead;
          !identical(record, null);
          record = record._next) {
        fn(record);
      }
    }
  