docs: @Override
      public boolean checkMgtKeyInUse(String CorpNum, MgtKeyType KeyType,
                                      String MgtKey) throws PopbillException {
  
          if (KeyType == null)
              throw new PopbillException(-99999999, "관리번호형태가 입력되지 않았습니다.");
          if (MgtKey == null || MgtKey.isEmpty())
              throw new PopbillException(-99999999, "관리번호가 입력되지 않았습니다.");
  
          try {
              TaxinvoiceInfo info = httpget("/Taxinvoice/" + KeyType.name() + "/"
                      + MgtKey, CorpNum, null, TaxinvoiceInfo.class);
  
              return (info.getItemKey() == null || info.getItemKey().isEmpty()) == false;
          } catch (PopbillException PE) {
              if (PE.getCode() == -11000005)
                  return false;
              throw PE;
          }
      }