docs: @Override
  	public FaxResult[] getFaxResult(String corpNum, String receiptNum)
  			throws PopbillException {
  		if (receiptNum == null)
  			throw new PopbillException(-99999999, "접수번호가 입력되지 않았습니다.");
  		if (receiptNum.length() != 18)
  			throw new PopbillException(-99999999, "접수번호가 올바르지 않았습니다.");
  
  		return httpget("/FAX/" + receiptNum, corpNum, null,
  				FaxResult[].class);
  	}