if ((s.length() > 1) && s.startsWith("0")) {
            return null;
        }
        return tryParseInt(s);
    }

    private static Integer tryParseInt(String s) {
        // for performance, check digits instead of relying later on catching NumberFormatException
        if (!isDigits(s)) {
            return null;
        }

        try {
            long longValue = Long.parseLong(s);