code: def toProtocolElement(self):
          
          ret = protocol.ReferenceSet()
          ret.assembly_id = pb.string(self.getAssemblyId())
          ret.description = pb.string(self.getDescription())
          ret.id = self.getId()
          ret.is_derived = self.getIsDerived()
          ret.md5checksum = self.getMd5Checksum()
          if self.getSpecies():
              term = protocol.fromJson(
                  json.dumps(self.getSpecies()), protocol.OntologyTerm)
              ret.species.term_id = term.term_id
              ret.species.term = term.term
          ret.source_accessions.extend(self.getSourceAccessions())
          ret.source_uri = pb.string(self.getSourceUri())
          ret.name = self.getLocalId()
          self.serializeAttributes(ret)
          return ret
docs: Returns the GA4GH protocol representation of this ReferenceSet.