如何解决错误“对象引用未设置为对象的实例”？

Question

我正在尝试根据用户指定隐藏按钮。登录后，我正在从数据库中获取“名称”。而Emp_Id来自页面遮罩。

没有任何想法。我这个Emp_Id没有得到。

namespace Board_Meeting.Pages
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Label User = (Label)Page.Master.FindControl("User_Name");

            if (Session["Emp_Id"] != null)
            {

                var cnnString = ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString;

                string User_Designation_Value = "Select Designation from [User] where Emp_id='" + User.Text + "'";
                string User_Designation;



                using (SqlConnection cnn = new SqlConnection(cnnString))
                {
                    cnn.Open();

                    SqlCommand Get_User_Designation = new SqlCommand(User_Designation_Value, cnn);
                    Get_User_Designation.CommandType = CommandType.Text;

                    User_Designation = Get_User_Designation.ExecuteScalar().ToString();



                }
            }
        }


        protected void Create_Agenda_Click(object sender, EventArgs e)
        {
            Response.Redirect("/Pages/CreateAgenda.aspx");
        }

        protected void B_View_Edit_Click(object sender, EventArgs e)
        {
            Response.Redirect("/Pages/EditAgenda.aspx");
        }

    }
}