ERROR - System.NullReferenceException: Object reference not set to an instance of an object

Line 47:         //}
Line 48:         //Profile.SCart.Insert(ProductID, Price, 1, ProductName, ProductImageUrl);
Line 49:         SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["techdata"].ToString());
Line 50:         SqlCommand cmd = new SqlCommand();
Line 51:         try

public partial class ProductDetails : System.Web.UI.Page
{
    //string yourname = TextBox1.Text.ToString();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["cart"] != null && Session["cart"] != "")
        {
            yourname.Visible = false;
        }
        else
        {
            yourname.Visible = true;
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        
        double Price = double.Parse(((Label)DataList1.Controls[0].FindControl("PriceLabel")).Text);
        string ProductName = ((Label)DataList1.Controls[0].FindControl("NameLabel")).Text;
        string ProductImageUrl = ((Label)DataList1.Controls[0].FindControl("ImageUrlLabel")).Text;
        string ProductID = ((HiddenField)DataList1.Controls[0].FindControl("HiddenField1")).ToString();
        //int ProductID;
        //if (Request.QueryString["ProductID"] != null) 
        //    ProductID = int.Parse(Request.QueryString["ProductID"].ToString());
        //if (Profile.SCart == null)
        //{
        //    Profile.SCart = new ShoppingCartExample.Cart();
        //    //Session["cart"] = SCart;
        //}
        //if (Session["cart"] != null)
        //{
        //    ClientScript.RegisterStartupScript(GetType(), "Message", "<SCRIPT LANGUAGE='javascript'>alert('CArt is available');</script>");
        //}
        //Profile.SCart.Insert(ProductID, Price, 1, ProductName, ProductImageUrl);
        SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["techdata"].ToString());
        SqlCommand cmd = new SqlCommand();
        try
            {
            conn.Open();
            cmd = conn.CreateCommand(); 
            if (cmd != null) { cmd.Dispose(); }
            cmd.CommandText = "INSERT INTO cart (ProductID,CustomerName, ProductName, " +
            "ProductImage, ProductPrice) VALUES ('" + ProductID + "','" + yourname.Text.ToString() + "','" + ProductName + "','" +
            ProductImageUrl + "','" + Price + "')";
            cmd.ExecuteNonQuery();
            conn.Close();
            Response.Redirect("~/Admin_Control/UpdateProductInfo.aspx");
            }
        catch (Exception ex)
        {
            ClientScript.RegisterStartupScript(GetType(), "Message", "<SCRIPT LANGUAGE='javascript'>alert('" + ex.ToString() + "');</script>");

        }
        //ClientScript.RegisterStartupScript(GetType(), "Message", "<SCRIPT LANGUAGE='javascript'>alert('Product added successfully');</script>");
        Session["cart"] = yourname.Text.ToString();
        Server.Transfer("product.aspx");
    }
}