public static @NotNull <K, V> MultiMap<K, V> createConcurrent() {
    return new MultiMap<K, V>(new ConcurrentHashMap<>()) {
      @Override
      protected @NotNull Collection<V> createCollection() {
        return ContainerUtil.createLockFreeCopyOnWriteList();
      }
    };
  }
public static @NotNull <K, V> MultiMap<K, V> createConcurrent()