code: @Override
      public String getMassPrintURL(String CorpNum, MgtKeyType KeyType,
                                    String[] MgtKeyList) throws PopbillException {
  
          return getMassPrintURL(CorpNum, KeyType, MgtKeyList, null);
      }
docs: /*
  (non-Javadoc)
  @see com.popbill.api.TaxinvoiceService#getMassPrintURL(java.lang.String, com.popbill.api.taxinvoice.MgtKeyType, java.lang.String[])