docs: public static int unitsToCalendarType(final String units) {
      if (units == null || units.isEmpty()) {
        throw new IllegalArgumentException("Units cannot be null or empty");
      }
      
      final String lc = units.toLowerCase();
      if (lc.equals("ms")) {
        return Calendar.MILLISECOND;
      } else if (lc.equals("s")) {
        return Calendar.SECOND;
      } else if (lc.equals("m")) {
        return Calendar.MINUTE;
      } else if (lc.equals("h")) {
        return Calendar.HOUR_OF_DAY;
      } else if (lc.equals("d")) {
        return Calendar.DAY_OF_MONTH;
      } else if (lc.equals("w")) {
        return Calendar.DAY_OF_WEEK;
      } else if (lc.equals("n")) {
        return Calendar.MONTH;
      } else if (lc.equals("y")) {
        return Calendar.YEAR;
      }
      throw new IllegalArgumentException("Unrecognized unit type: " + units);
    }