Delete ไม่ได้ ติดError NullReferenceException was unhandled by user code Object reference not set to an instance of an object.

  Dim lblID As Label = CType(gvManage.FindControl("lblID"), Label)
        BookID = lblID.Text
        strSQL = " DELETE FROM Book Where BookID = '" &  BookID & "' "
      
        objCmd = New SqlCommand(strSQL, objConn)
        objCmd.ExecuteNonQuery()

        gvManageBindData()

Protected Sub gvManage_RowDeleting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles gvManage.RowDeleting
        strSQL = "DELETE FROM Book WHERE BookID = '" & gvManage.DataKeys.Item(e.RowIndex).Value & "'"
        objCmd = New SqlCommand(strSQL, objConn)
        objCmd.ExecuteNonQuery()

        gvManageBindData()

    End Sub