Need string if har row to show value, else to be ----

Question

Need string if har row to show value, else to be ----

I try this

What I wrong?

 

string redni_broj = "";
           using (SqlConnection openCon8 = new SqlConnection(Con))
           {
               SqlDataReader reader8;
               SqlCommand cmd8 = new SqlCommand();
               cmd8.CommandText = "select FORMAT(redni_broj, '00000') from mp_faktura_lista where id=" + id_fakture;
               cmd8.Connection = openCon8;
               openCon8.Open();
               reader8 = cmd8.ExecuteReader();
               if (reader8.HasRows)
               {
                   while (reader8.Read())
                   {
                       redni_broj = reader8[0].ToString();
                   }
               }
               else
               {
                   redni_broj = "-----";
               }
               openCon8.Close();
           }