code: def referencesGenerator(self, request):
          
          referenceSet = self.getDataRepository().getReferenceSet(
              request.reference_set_id)
          results = []
          for obj in referenceSet.getReferences():
              include = True
              if request.md5checksum:
                  if request.md5checksum != obj.getMd5Checksum():
                      include = False
              if request.accession:
                  if request.accession not in obj.getSourceAccessions():
                      include = False
              if include:
                  results.append(obj)
          return self._objectListGenerator(request, results)
docs: Returns a generator over the (reference, nextPageToken) pairs
          defined by the specified request.