public IActionResult Add(KVmodel kvmodel)
        {
            if (kvmodel.Text != null)
            {
                string[] values = kvmodel.Text.Split('=');
                if (values.Length == 2)
                {
                    keyValueList.AddPair(values[0], values[1]);
                }
                else
                {
                    string text = "Bad format: item must consist of a single key value pair separated by '='";
                    return(RedirectToAction("Error", new ErrorViewModel {
                        Text = text
                    }));
                }
            }
            var model = new KVmodel(keyValueList.DisplayList);

            return(RedirectToAction("Index", model));
        }