code: private void crossCheck() {
          // only cross-check date, time and date-time
          // avoid object creation if possible
          if (date != null) {
              crossCheck(date);
          }
          if (time != null) {
              crossCheck(time);
              if (date != null && fieldValues.size() > 0) {
                  crossCheck(date.atTime(time));
              }
          }
      }
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