@Override
  public void add(@NotNull K key, @NotNull V value) {
    ConcurrentMap<K, Object> map = (ConcurrentMap<K, Object>)myMap;
    while (true) {
      Object current = map.get(key);
      if (current == null) {
        if (ConcurrencyUtil.cacheOrGet(map, key, value) == value) {
          break;
        }
      }
      else if (current instanceof MostlySingularMultiMap.ValueList) {
        List<?> curList = (ValueList<?>)current;
        List<Object> newList = new ValueList<>(curList.size() + 1);
        newList.addAll(curList);
        newList.add(value);
        if (map.replace(key, curList, newList)) break;
      }
      else {
        List<Object> newList = new ValueList<>(2);
        newList.add(current);
        newList.add(value);
        if (map.replace(key, current, newList)) break;
      }
    }
  }
@Override
  public void add(@NotNull K key, @NotNull V value)