code: def referenceSetsGenerator(self, request):
          
          results = []
          for obj in self.getDataRepository().getReferenceSets():
              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 request.assembly_id:
                  if request.assembly_id != obj.getAssemblyId():
                      include = False
              if include:
                  results.append(obj)
          return self._objectListGenerator(request, results)
docs: Returns a generator over the (referenceSet, nextPageToken) pairs
          defined by the specified request.