code: @Override
    public DurationFormatter getFormatter() {
      if (f == null) {
        if (fallback != null) {
          fallback = fallback.withLocale(localeName).withTimeZone(timeZone);
        }
        formatter = getPeriodFormatter();
        builder = getPeriodBuilder();
  
        f = createFormatter();
      }
      return f;
    }
docs: Return a formatter based on this factory's current settings.
  
  @return a BasicDurationFormatter