docs: @Override
      public String getMassPrintURL(String CorpNum, MgtKeyType KeyType,
                                    String[] MgtKeyList, String UserID) throws PopbillException {
          if (KeyType == null)
              throw new PopbillException(-99999999, "관리번호형태가 입력되지 않았습니다.");
          if (MgtKeyList == null || MgtKeyList.length == 0)
              throw new PopbillException(-99999999, "관리번호 목록이 입력되지 않았습니다.");
  
          String PostData = toJsonString(MgtKeyList);
  
          URLResponse response = httppost("/Taxinvoice/" + KeyType.name()
                  + "?Print", CorpNum, PostData, UserID, URLResponse.class);
  
          return response.url;
      }