@Override
 public List<ExternalId> visitCreditDefaultSwapOptionSecurity(
     final CreditDefaultSwapOptionSecurity security) {
   final CreditDefaultSwapSecurity underlyingCDS =
       (CreditDefaultSwapSecurity)
           _securitySource.getSingle(
               ExternalIdBundle.of(security.getUnderlyingId())); // TODO version
   final ExternalId regionId = underlyingCDS.getRegionId();
   final String securityType = security.getSecurityType();
   return Arrays.asList(
       ExternalId.of(SECURITY_IDENTIFIER, securityType + SEPARATOR + regionId.getValue()));
 }