code: @Override
      public Response cancelReserveRN(String CorpNum, String requestNum) throws PopbillException {
          return cancelReserveRN(CorpNum, requestNum, null);
      }
docs: /*
  (non-Javadoc)
  @see com.popbill.api.MessageService#cancelReserveRN(java.lang.String, java.lang.String)