Problem in Null object

Question

Greeting

I used gridview in my system to  review users, anyway when I need to delete user, I need to deleted all rows in many tables depends on UserId. Actually I created a stored procedure  take an input parameter (UserId) from gridview.

See gridview code herer

      <asp:GridView ID="gvbremployee" runat="server" AllowSorting="True" AutoGenerateColumns="False" Font-Size="Medium" Width="60%" DataKeyNames="UserId" DataSourceID="SDS_BR_DLL" EmptyDataText="Sorry! No staff in selected branch." OnSelectedIndexChanged="gvbremployee_SelectedIndexChanged" OnRowDeleting="gvbremployee_RowDeleting">

          <Columns>
              <asp:TemplateField ShowHeader="False">
                  <ItemTemplate>
                      <asp:LinkButton ID="LnkBtn_Sel" runat="server" CausesValidation="False" CommandName="Select" class="btn btn-outline-primary"><i class="fa fa-folder-open"></i></asp:LinkButton>
                      <asp:LinkButton ID="LnkBtn_del" runat="server" CausesValidation="False" CommandName="Delete" OnClientClick="return confirm('Are you sure you want to delete Employee row?')" class="btn btn-outline-danger"><i class="fa fa-trash" aria-hidden="true"></i></asp:LinkButton>
                  </ItemTemplate>
              </asp:TemplateField>
              <asp:BoundField DataField="UserId" Visible="False" HeaderText="UserId" />

              <asp:BoundField DataField="UserName" HeaderText="UserName"/>

              <asp:BoundField DataField="S_Gender" HeaderText="Gender" SortExpression="S_Gender" />
              <asp:BoundField DataField="S_Salary" HeaderText="Salary" SortExpression="S_Salary" />
<asp:CheckBoxField DataField="S_Status" HeaderText="Status" SortExpression="S_Status" />
          </Columns>
      </asp:GridView>

Code behide for delete user event in gridview 

protected void gvbremployee_RowDeleting(object sender, GridViewDeleteEventArgs e)
{

    try
    {
        GridViewRow row = (GridViewRow)gvbremployee.Rows[e.RowIndex];
    string idvalue = gvbremployee.DataKeys[row.RowIndex].Values["UserId"].ToString();

        using (SqlConnection sqlcon = new SqlConnection(Constr))
        {

            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["Constr"].ConnectionString);

            SqlCommand comm = new SqlCommand();
            comm.CommandText = "del_user"; //this stored procedure and has an ID called UserId
            comm.CommandType = CommandType.StoredProcedure;
            //Pass the value here
            comm.Parameters.AddWithValue("@UserId", idvalue);
            comm.Connection = conn;

            conn.Open();
            comm.ExecuteNonQuery();
            conn.Close();
        }
    }
    catch (Exception ex)
    {
         Lbinfo.Text = ex.Message;
        Lbinfo.ForeColor = System.Drawing.Color.Red;

    }

}

 Stored Procedure code

 

CREATE PROCEDURE [dbo].[del_user]

AS
        DECLARE @UserId uniqueidentifier
    SET @UserId = 'THE GUID OF THE USER HERE'

   DELETE FROM Profiles WHERE UserId = @UserId
   DELETE FROM UsersInRoles WHERE UserId = @UserId
   DELETE FROM Memberships WHERE UserId = @UserId
   DELETE FROM Users WHERE UserId = @UserId
   DELETE FROM Staff WHERE UserId = @UserId
RETURN 0

When I execute app. and delete user an error messge is:

 

Object reference not set to an instance of an object.

 

That's mean a null in send parameter to stored procedure

 

A first chance exception of type 'System.NullReferenceException' occurred in WebApplication1.dll , can not able to catch (UserId) Valye

 

I change method

string idvalue = gvbremployee.DataKeys[row.RowIndex].Values["UserId"].ToString();

to

object idvalue = gvbremployee.Rows[e.RowIndex].Cells[0].UniqueID;

 

So what a problem, please.

Many thanks