FindControl in GridView RowUpdating Event Error: Object reference not set to an instance of an object

When i updating dropdownlist in gridview, having this error.

Object reference not set to an instance of an object

string NamDept = (GridView.Rows[e.RowIndex].FindControl("ddIDDEPT") as DropDownList).SelectedItem.Value;

Here is complete coding

HTML

            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
                AutoGenerateEditButton="True" OnRowDataBound="GridView1_RowDataBound" 
                OnRowEditing="GridView1_RowEditing" DataKeyNames="EmpID" 
                OnRowCancelingEdit="GridView1_RowCancelingEdit"
                CssClass="gridv" OnRowUpdating="GridView1_RowUpdating">
                <Columns>
                   <asp:TemplateField HeaderText="Department">
                        <EditItemTemplate>
                            <asp:DropDownList id="ddlIDDEPT" CssClass="dropdown" runat="server">
                                </asp:DropDownList>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="ddlIDDEPT" runat="server" Text='<% #Eval("NamDept") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="SubDepartment">
                        <EditItemTemplate>
                            <asp:DropDownList id="ddlSubDepartment" runat="server">
                                </asp:DropDownList>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="ddlSubDepartment" runat="server" Text='<% #Eval("NamSubDept") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Designation">
                        <EditItemTemplate>
                            <asp:DropDownList id="ddlDesignation"  runat="server" Text='<% #Eval("NamDesig") %>'>
                                </asp:DropDownList>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="ddlDesignation" runat="server" Text='<% #Eval("NamDesig") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>  
            </asp:GridView>

        protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            string NamDept = (GridView1.Rows[e.RowIndex].FindControl("ddlDepartment") as DropDownList).SelectedItem.Value;

            int IDdept = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value.ToString());
            SqlConnection con = new SqlConnection("Data Source=IT;Integrated Security=SSPI;Initial Catalog=AttendanceManagement");
            {
                string query = "UPDATE Department SET NamDept = @NamDept WHERE IDdept = @IDdept";
                SqlCommand cmd = new SqlCommand(query, con);
                {
                    cmd.Parameters.AddWithValue("@NamDept", NamDept);
                    cmd.Parameters.AddWithValue("@IDdept", IDdept);
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }
        }

pleas guide ...