Как проверить нулевое значение gridview

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Мой код выглядит следующим образом

частный недействительными SaveCheckedValues()
{
Система.Коллекции.Userdetails коллекции = новый
Система.Коллекции.список ArrayList();
индекс int = -1;
по каждому элементу (gvrow GridViewRow в grdRpt.Строк)
{
индекс = конвертировать.ToInt32(grdRpt.DataKeys[gvrow.Параметр rowindex].Значение);

 bool result = ((CheckBox)gvrow.FindControl("chkselecdata")).Checked;

               
                if (Session["CHECKED_ITEMS"] != null)
                    userdetails = (System.Collections.ArrayList)Session["CHECKED_ITEMS"];
                if (result)
                {
                    if (!userdetails.Contains(index))
                        userdetails.Add(index);
                }
                else
                    userdetails.Remove(index);
            }
            if (userdetails != null && userdetails.Count > 0)
                Session["CHECKED_ITEMS"] = userdetails;
        }

when i run the above code shows error as follows

Object cannot be cast from DBNull to other types.

The error shows in below line as follows

 index = Convert.ToInt32(grdRpt.DataKeys[gvrow.RowIndex].Value);


 In the gridview as follows

 selectdata  transacteeid     Qty   Price Isactive

  checkbox                      6      25       1
  checkbox                      4      20       1
  checkbox  109453628727        1      8        1
  checkbox  109453628727        2      6        1
  checkbox  109453628727        3      7        1
  checkbox  109453628727        5      2        1
  checkbox  109453628727        1      5        1

how to fix this error.

 in the gridview first two rows values is empty. because of this shows error. i think.

 how to validate this null value in the gridview.

What I have tried:

My code as follows

  private void SaveCheckedValues()
        {
             System.Collections.ArrayList userdetails = new 
             System.Collections.ArrayList();
            int index = -1;
            foreach (GridViewRow gvrow in grdRpt.Rows)
            {
              index = Convert.ToInt32(grdRpt.DataKeys[gvrow.RowIndex].Value);
              <pre> bool result = ((CheckBox)gvrow.FindControl("chkselecdata")).Checked;

               
                if (Session["CHECKED_ITEMS"] != null)
                    userdetails = (System.Collections.ArrayList)Session["CHECKED_ITEMS"];
                if (result)
                {
                    if (!userdetails.Contains(index))
                        userdetails.Add(index);
                }
                else
                    userdetails.Remove(index);
            }
            if (userdetails != null && userdetails.Count > 0)
                Session["CHECKED_ITEMS"] = userdetails;
        }

when i run the above code shows error as follows

Object cannot be cast from DBNull to other types.

The error shows in below line as follows

 index = Convert.ToInt32(grdRpt.DataKeys[gvrow.RowIndex].Value);


 In the gridview as follows

 selectdata  transacteeid     Qty   Price Isactive

  checkbox                      6      25       1
  checkbox                      4      20       1
  checkbox  109453628727        1      8        1
  checkbox  109453628727        2      6        1
  checkbox  109453628727        3      7        1
  checkbox  109453628727        5      2        1
  checkbox  109453628727        1      5        1

how to fix this error.

 in the gridview first two rows values is empty. because of this shows error. i think.

 how to validate this null value in the gridview.

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