docs: @Override
      public IssueResponse registIssue(String CorpNum, Taxinvoice taxinvoice,
                                  Boolean WriteSpecification, String Memo, Boolean ForceIssue,
                                  String DealInvoiceKey, String EmailSubject, String UserID)
              throws PopbillException {
  
          if (taxinvoice == null)
              throw new PopbillException(-99999999, "세금계산서 정보가 입력되지 않았습니다.");
  
          if (WriteSpecification)
              taxinvoice.setWriteSpecification(true);
  
          if (Memo != null)
              taxinvoice.setMemo(Memo);
  
          if (ForceIssue)
              taxinvoice.setForceIssue(true);
  
  
          if (DealInvoiceKey != null)
              taxinvoice.setDealInvoiceMgtKey(DealInvoiceKey);
  
          if (EmailSubject != null)
              taxinvoice.setEmailSubject(EmailSubject);
  
          String PostData = toJsonString(taxinvoice);
  
  
          return httppost("/Taxinvoice", CorpNum, PostData,
                  UserID, "ISSUE", IssueResponse.class);
      }