code: private static void updateCheckConflict(
              Map<TemporalField, Long> fieldValues,
              TemporalField targetField,
              TemporalField changeField,
              long changeValue) {
          
          Long old = fieldValues.put(changeField, changeValue);
          if (old != null && changeValue != old.longValue()) {
              throw new DateTimeException(
                      "Conflict found: " + changeField + " " + old +
                      " differs from " + changeField + " " + changeValue +
                      " while resolving  " + targetField);
          }
      }
docs: -------------------------------------------------------------------------