Object reference not set to an instance of an object. error show using file upload control in gridview

protected void Button1_Click(object sender, EventArgs e)
        {
           
            Button Button1 = (Button)sender;
            GridViewRow gvRow = (GridViewRow)Button1.NamingContainer;
            FileUpload fuCOA = (FileUpload)gvRow.FindControl("FileUpload1");
            Stream fs = fuCOA.PostedFile.InputStream;
            BinaryReader br = new BinaryReader(fs);
            Byte[] bytes = br.ReadBytes((Int32)fs.Length);
            Label ID = ((Label)gvRow.FindControl("lblApplicantNo"));
            string sql_update = @" update ApplicantData set ApplicantFile=@ApplicantFile";
            sql_update += " where ApplicantNo=@ApplicantNo";
             SqlCommand cmdDist = new SqlCommand(sql_update, con);
            
             cmdDist.Parameters.Add("@ApplicantFile", SqlDbType.Binary).Value = bytes;
             cmdDist.Parameters.AddWithValue("@ApplicantNo", ID.Text.ToString());
                con.Open();
                int i = cmdDist.ExecuteNonQuery();
                con.Close();
                if (i > 0)
                {
                    Response.Redirect("ApplicantExamUpdate.aspx");
                }
           
        }