code: @Override
  	public Response update(String CorpNum, String MgtKey, Cashbill cashbill,
  			String UserID) throws PopbillException {
  		if (MgtKey == null || MgtKey.isEmpty())
  			throw new PopbillException(-99999999, "관리번호가 입력되지 않았습니다.");
  
  		String PostData = toJsonString(cashbill);
  
  		return httppost("/Cashbill/"+MgtKey, CorpNum,
  				PostData, UserID, "PATCH", Response.class);
  	}
docs: /* (non-Javadoc)
  @see com.popbill.api.CashbillService#update(java.lang.String, java.lang.String, com.popbill.api.cashbill.Cashbill, java.lang.String)