docs: public static void setTimeZone(final SimpleDateFormat fmt,
                                    final String tzname) {
      if (tzname == null) {
        return;  // Use the default timezone.
      }
      final TimeZone tz = DateTime.timezones.get(tzname);
      if (tz != null) {
        fmt.setTimeZone(tz);
      } else {
        throw new IllegalArgumentException("Invalid timezone name: " + tzname);
      }
    }