Systemnullreferenceexception in ASP.NET и код до диез

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Text;
using System.Messaging;
using System.Net;
using System.Net.Mail;
namespace exam
{
    public partial class GetFillFromStudent : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Page c = (Page)Context.Handler;


            Label8.Text =  ((Label)c.FindControl("Label1")).Text;
            Label3.Text =  ((Label)c.FindControl("Label1")).Text;
            Label2.Text = "monaxshroog@gmail.com";
            Label4.Text = ((TextBox)c.FindControl("DatabaseG")).Text;
            Label5.Text = ((TextBox)c.FindControl("NetworkG")).Text;
            Label6.Text = ((TextBox)c.FindControl("AnalysisG")).Text;
            Label7.Text = ((TextBox)c.FindControl("hour")).Text;
           

            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["seniorConnectionString"].ConnectionString);
            con.Open();

            SqlCommand com = new SqlCommand("select*from dbo.Student", con);
            if (!String.IsNullOrEmpty(Request.QueryString["pID"]))
            {
                int thePID = Convert.ToInt32(Request.QueryString["pID"]);
            }
            SqlDataReader dr;
            dr = com.ExecuteReader();
            if (dr.HasRows == true)
            { 

                dr.Close();
            }
            con.Close();

            List labels = new List();
            for (int i = 0; i <= 6; i++)
            {
                Label label = new Label();
                labels.Add(label);
            }





            con.Open();
            com.ExecuteNonQuery();
            SqlDataAdapter sda = new SqlDataAdapter(com);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            com.ExecuteNonQuery();
            con.Close();

        }

        protected void Button1_Click(object sender, EventArgs e)
        {

            using (MailMessage mailMessage = new MailMessage(ConfigurationManager.AppSettings["SMTPuser"], Label2.Text))
            {

                mailMessage.Subject = "student";
                mailMessage.Body = "Hello amal you can log in the system This your ID:18819 username :amal";
                using (SmtpClient smtp = new SmtpClient())
                {
                    smtp.EnableSsl = true;
                    smtp.Host = ConfigurationManager.AppSettings["Host"];
                    smtp.EnableSsl = Convert.ToBoolean(ConfigurationManager.AppSettings["EnabelSSL"]);
                    NetworkCredential networkCred = new NetworkCredential(ConfigurationManager.AppSettings["SMTPuser"], ConfigurationManager.AppSettings["SMTPpassword"]);

                    smtp.UseDefaultCredentials = true;
                    smtp.Credentials = networkCred;
                    smtp.Port = int.Parse(ConfigurationManager.AppSettings["Port"]);
                    smtp.Send(mailMessage);
                    ClientScript.RegisterStartupScript(GetType(), "alter", "alter(Email sent);", true);

                }
            }
        }

        protected void Button2_Click(object sender, EventArgs e)
        {

            using (MailMessage mailMessage = new MailMessage(ConfigurationManager.AppSettings["SMTPuser"], Label2.Text))
            {

                mailMessage.Subject = "student";
                mailMessage.Body = "Hello amal you can log in the system This your ID:18819 username :amal";
                using (SmtpClient smtp = new SmtpClient())
                {
                    smtp.EnableSsl = true;
                    smtp.Host = ConfigurationManager.AppSettings["Host"];
                    smtp.EnableSsl = Convert.ToBoolean(ConfigurationManager.AppSettings["EnabelSSL"]);
                    NetworkCredential networkCred = new NetworkCredential(ConfigurationManager.AppSettings["SMTPuser"], ConfigurationManager.AppSettings["SMTPpassword"]);

                    smtp.UseDefaultCredentials = true;
                    smtp.Credentials = networkCred;
                    smtp.Port = int.Parse(ConfigurationManager.AppSettings["Port"]);
                    smtp.Send(mailMessage);
                    ClientScript.RegisterStartupScript(GetType(), "alter", "alter(Email sent);", true);
                }
            }
        }
    }
}