code: public LocalDate getCalendarServiceRangeStart() {
  
          int startDate = 0;
          for (Service service : feed.services.values()) {
              if (service.calendar == null)
                  continue;
  //            if (startDate == 0 || service.calendar.start_date < startDate) {
  //                startDate = service.calendar.start_date;
  //            }
          }
          if (startDate == 0)
              return null;
  
          DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMdd");
          return LocalDate.parse(String.valueOf(startDate), formatter);
      }
docs: returns null for schedules without calendar service schedules