NullReferenceException i am familiar with them, but cannot solve on this occasion

Question

im fairly new to ASP.net but i am familiar with Null reference exceptions however i cant solve this one. Im trying to collect data from a webform and pass it to my database through a connection string, this is when the exception occurs.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;


public partial class Register : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            if (IsPostBack)
            {
                SqlConnection studConnA = new SqlConnection(ConfigurationManager.ConnectionStrings["StudConnection"].ConnectionString);
                studConnA.Open();
                string checkuser = "select count(*) from StudTable where Name='" + TextBoxName.Text + "'";
                SqlCommand studComA = new SqlCommand(checkuser, studConnA);
                int temp = Convert.ToInt32(studComA.ExecuteScalar().ToString());
                if (temp == 1)
                {
                    Response.Write("User already Exists");
                }
                studConnA.Close();
            }

        }
        catch (Exception ex)
        {
            Response.Write("Error:" + ex.ToString());
        }
    }


    protected void Button1_Click(object sender, System.EventArgs e)
    {
        try
        {
            SqlConnection studConn = new SqlConnection(ConfigurationManager.ConnectionStrings["StudConnectionString"].ConnectionString);
            studConn.Open();
            string insertQuery = "insert into StudTable (Name,Email,Age,Continent,School,Password) values (@name,@email,@age,@cont,@school,@pass)";
            SqlCommand studCom = new SqlCommand(insertQuery, studConn);
            studCom.Parameters.AddWithValue("@name", TextBoxName.Text);
            studCom.Parameters.AddWithValue("@email", TextBoxEmail.Text);
            studCom.Parameters.AddWithValue("@age", TextBoxAge.Text);


studCom.Parameters.AddWithValue("@cont",DropDownCont.SelectedItem.ToString());
            studCom.Parameters.AddWithValue("@school", TextBoxSchool.Text);
            studCom.Parameters.AddWithValue("@pas", TextBoxPass.Text);

            studCom.ExecuteNonQuery();
            Response.Redirect("Backend.aspx");
            Response.Write("Your Registration is Sucessful");

            studConn.Close();
        }
        catch (Exception ex)
        {
            Response.Write("Error:" +ex.ToString());
        }
    }
}

The null reference occurs at line 19

Line 17:                 if (IsPostBack)
Line 18:                 {
Line 19:                     SqlConnection studConnA = new SqlConnection(ConfigurationManager.ConnectionStrings["StudConnection"].ConnectionString);
Line 20:                     studConnA.Open();
Line 21:                     string checkuser = "select count(*) from StudTable where Name='" + TextBoxName.Text + "'";

I believe the issue is in the syntax of my connection string but im not sure,

Can anyone help me to solve this?

Answer 1

Check your configuration file for the following key:

<connectionStrings>
 <add name="StudConnection" connectionString="YOUR DETAILS" />
</connectionStrings>

If it doesn't exist, add the right key and retry.

You can also check the issue with the following code:

   if (IsPostBack)
    {
        // if this line fails, then you don't have the proper connection string
        // element in the config file.
        Debug.Assert(ConfigurationManager.ConnectionStrings["StudConnection"] != null);

        SqlConnection studConnA = new SqlConnection(ConfigurationManager.ConnectionStrings["StudConnection"].ConnectionString);
        studConnA.Open();
        string checkuser = "select count(*) from StudTable where Name='" + TextBoxName.Text + "'";
        SqlCommand studComA = new SqlCommand(checkuser, studConnA);
        int temp = Convert.ToInt32(studComA.ExecuteScalar().ToString());
        if (temp == 1)
        {
            Response.Write("User already Exists");
        }
        studConnA.Close();
    }

Answer 2

It would appear that there is no connection string named StudConnection configured.