docs: public int compare(final SnomedConcept o1, final SnomedConcept o2) {
          if (o1 == o2) return 0;
          if (o1 != null) {
              if (o2 == null) return 1;
              else return o1.candidatePreferred.compareTo(o2.candidatePreferred);
          }
          return -1;
      }