docs: public static HashFunction concatenating(
        HashFunction first, HashFunction second, HashFunction... rest) {
      // We can't use Lists.asList() here because there's no hash->collect dependency
      List<HashFunction> list = new ArrayList<HashFunction>();
      list.add(first);
      list.add(second);
      for (HashFunction hashFunc : rest) {
        list.add(hashFunc);
      }
      return new ConcatenatedHashFunction(list.toArray(new HashFunction[0]));
    }