class DateTimeExt {

    public static String toUtcDateTimeString(long msSinceEpoch) {
        if (msSinceEpoch == 0L) {
            return null;
        }
        return ISO_UTC_DATE_TIME_FORMATTER.format(Instant.ofEpochMilli(msSinceEpoch)) + 'Z';
    }

    private  DateTimeExt();

}