anchor.diff:      });
     }
   
  -  V operator [](Object key) {
  +  V? operator [](Object? key) {
       return JS('var', '#.get(#)', _map, key);
     }
   
  
positive.code:   Node _splayMax(Node node) {
      Node current = node;
      while (current.right != null) {
        Node right = current.right;
        current.right = right.left;
        right.left = current;
        current = right;
  
negative.code:   }
  
    void _filterWhere(bool test(E element), bool removeMatching) {
      _LinkedHashSetCell? cell = _first;
      while (cell != null) {
        E element = cell._element;
        _LinkedHashSetCell? next = cell._next;
        int modifications = _modifications;
        bool shouldRemove = (removeMatching == test(element));
        if (modifications != _modifications) {
  