anchor.diff:        throw StateError('Data is in the process of being created.');
       }
       for (int index = 0; index < _list.length; index++) {
  -      E entity = _list[index];
  +      final entity = _list[index] as E0?;
         if (entity != null) {
  -        f(entity, _data[index]);
  +        f(entity, _data[index] as D0);
         }
       }
     }
  
positive.code:   bool _closed = false;
  
    int _size = 0;
    final List<E> _list = <E>[];
  
    /// Returns the [index]th entity in the map.
    E getEntity(int index) => _list[index];
  
    /// Returns the number of non-null entities in the map.
    int get size => _size;
  
negative.code:       throw StateError('Env is in the process of being created.');
      }
      for (int index = 0; index < _list.length; index++) {
        final entity = _list[index] as E0?;
        if (entity != null) {
          f(entity, _data[index] as D0, _env[index] as V0);
        }
      }
    }
  