object reference not set to an instance of an object problem which object is the compiler referring?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using System.Data;
using System.Data.SqlClient;
using System.IO;

namespace hrms_hrmodule
{
    /// <summary>
    /// Interaction logic for Register.xaml
    /// </summary>
    public partial class Register : Window
    {
        public SqlConnection con;
        public SqlCommand cmd;
        public byte[] doc1, doc2, pic1;
        public string sex;
        public Register()
        {
            InitializeComponent();

        }
        private void load_data(object sender, RoutedEventArgs e)
        {


        }

        private void back(object sender, RoutedEventArgs e)
        {
            MainWindow main = new MainWindow();
            this.Hide();
            main.Show();
        }
        public void loadimage(object sender, RoutedEventArgs e)
        {
            Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
            dlg.ShowDialog();
            FileStream fs = new FileStream(dlg.FileName, FileMode.Open, FileAccess.Read);
            Byte[] pic1 = new Byte[fs.Length];
            fs.Read(pic1, 0, Convert.ToInt32(fs.Length));
            text_photo.Text = dlg.SafeFileName.ToString();


        }
        public void loaddoc1(object sender, RoutedEventArgs e)
        {
            Microsoft.Win32.OpenFileDialog flg = new Microsoft.Win32.OpenFileDialog();
            flg.ShowDialog();
            FileStream fd = new FileStream(flg.FileName, FileMode.Open, FileAccess.Read);
            Byte[] doc1 = new Byte[fd.Length];
            fd.Read(doc1, 0, Convert.ToInt32(fd.Length));       
            text_doc1.Text = flg.SafeFileName.ToString();
        }
        public void loaddoc2(object sender, RoutedEventArgs e)
        {
            Microsoft.Win32.OpenFileDialog fl = new Microsoft.Win32.OpenFileDialog();
            fl.ShowDialog();
            FileStream fg = new FileStream(fl.FileName, FileMode.Open, FileAccess.Read);
            
            Byte[] doc2 = new Byte[fg.Length];
            fg.Read(doc2, 0, Convert.ToInt32(fg.Length));
            text_doc2.Text = fl.SafeFileName.ToString();
        }
        public void savedata(object sender, RoutedEventArgs e)
        {
            con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=E:\Software\Hrms\hrms_hrmodule\hrms_hrmodule\employee.mdf;Integrated Security=True;");
            try
            {
                con.Open();
                string s = "insert into Registration values(@empid,@name,@age,@dob,@add,@contact,@sex,@skill,@prof,@photo,@doc1,@doc2)";

                cmd.Parameters.Add(new SqlParameter("@empid",SqlDbType.Int));
                cmd.Parameters.Add(new SqlParameter("@name",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@age", SqlDbType.Int));
                cmd.Parameters.Add(new SqlParameter("@dob", SqlDbType.Date));
                cmd.Parameters.Add(new SqlParameter("@add",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@contact",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@sex",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@skill",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@prof",SqlDbType.Text));
                cmd.Parameters.Add(new SqlParameter("@photo",SqlDbType.Image));
                cmd.Parameters.Add(new SqlParameter("@doc1",SqlDbType.Image));
                cmd.Parameters.Add(new SqlParameter("@doc2", SqlDbType.Image));

                cmd.Parameters["@empid"].Value = text_id.Text;
                cmd.Parameters["@name"].Value = text_name.Text;
                cmd.Parameters["@age"].Value = text_age.Text;
                cmd.Parameters["@add"].Value = text_address.Text;
                cmd.Parameters["@contact"].Value = text_contact.Text;
                cmd.Parameters["@dob"].Value = datepicker.Text;
                cmd.Parameters["@prof"].Value = comboBox1.Text;
                cmd.Parameters["@skill"].Value =comboBox.Text;
                cmd.Parameters["@photo"].Value = pic1;
                cmd.Parameters["@doc1"].Value = doc1;
                cmd.Parameters["@doc2"].Value = doc2;
                cmd.Parameters["@sex"].Value = combo_sex.Text;
                cmd = new SqlCommand(s,con);
                cmd.ExecuteNonQuery();
                MessageBox.Show("record saved");
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);

            }
          }
             
    
 
    }
}