string IsNullOrEmpty
string queryStringValue = Request.QueryString["key"];
if (string.IsNullOrEmpty(queryStringValue)) {
// querystring not supplied. Do necessary action
}
else
// Querystring supplied. continue execution
string queryStringValue = Request.QueryString["key"];
if (string.IsNullOrEmpty(queryStringValue)) {
// querystring not supplied. Do necessary action
}
else
// Querystring supplied. continue execution