code: public static void addModificationTimeToAttributes(Map<String, byte[]> attributes, Clock clock) {
      attributes.put(FILE_MODIFICATION_TIMESTAMP_KEY, Longs.toByteArray(clock.currentTimeMillis()));
    }
docs: Add a key and value representing the current time, as determined by the passed clock, to the
  passed attributes dictionary.
  @param attributes The file attributes map to update
  @param clock The clock to retrieve the current time from