code: static boolean isZipDirectory(Key key) {
      Iced ice = DKV.getGet(key);
      if (ice == null) throw new H2OIllegalArgumentException("Missing data", "Did not find any data under " +
              "key " + key);
      ByteVec bv = (ByteVec) (ice instanceof ByteVec ? ice : ((Frame) ice).vecs()[0]);
  
      return isZipDirectory(bv);
    }
docs: This method check if the input argument is a zip directory containing files.
  
  @param key
  @return true if bv is a zip directory containing files, false otherwise.