anchor.diff:    }
   
     @override
  -  V operator [](Object key) {
  +  V? operator [](Object? key) {
       if (_extra == null) {
         return (_key == key) ? _value : null;
       } else if (_MARKER == _extra) {
  
positive.code:   final List _list;
    int _remaining;
    int _index = 0;
    K _current;
  
    _MapletListIterator(this._list, this._remaining);
  
    @override
    K get current => _current;
  
    @override
    bool moveNext() {
  
negative.code:     } else {
        int remaining = _extra;
        int index = 0;
        int copyTo = 0;
        int copyFrom = 0;
        while (remaining > 0 && index < CAPACITY) {
          var candidate = _key[index];
          if (_MARKER == candidate) {
  