Gridview中RadioButtonList联动中“未将对象引用设置到对象的实例”
建站中，点击更新时怀疑RadioButtonList取值没成功，望各位大大帮忙看看
源错误: 


行 147: {
行 148: string id = e.CommandArgument.ToString();
行 149: string audit = auditrbl.SelectedItem.Value.ToString();
行 150: string level = levelrbl.SelectedItem.Value.ToString();
行 151: string str = "UPDATE T_Member SET [F_Audit]=" + audit + ",[F_Level]=" + level + ";";

源文件: j:\Sam‘s Work1\MemberMain.aspx.cs 行: 149 

堆栈跟踪: 


[NullReferenceException: 未将对象引用设置到对象的实例。]
  MemberMain.GridView_RowCommand(Object sender, GridViewCommandEventArgs e) in j:\Sam‘s Work1\MemberMain.aspx.cs:149
  System.Web.UI.WebControls.GridView.OnRowCommand(GridViewCommandEventArgs e) +108
  System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +112
  System.Web.UI.WebControls.GridView.OnBubbleEvent(Object source, EventArgs e) +95
  System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37
  System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +123
  System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37
  System.Web.UI.WebControls.Button.OnCommand(CommandEventArgs e) +118
  System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +166
  System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
  System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
  System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
  System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

HTML code

 <asp:TemplateField HeaderText="审核状态">
                        <ItemTemplate>
                                <asp:Label ID="lblaudit" runat="server" Text='<%# Eval("F_Audit") %>' />
                        </ItemTemplate>
                        <EditItemTemplate>
                                <asp:RadioButtonList ID="AuditRBL" runat="server" RepeatDirection="Vertical" AutoPostBack="true" AppendDataBoundItems="true">
                                    <asp:ListItem Value="0" Text="未通过"></asp:ListItem>
                                    <asp:ListItem Value="1" Text="已通过"></asp:ListItem>
                                </asp:RadioButtonList>
                        </EditItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="级别">
                        <ItemTemplate>
                                <asp:Label  ID="lbllevel"  runat="server"  Text='<%# Eval("F_Level") %>' ></asp:Label>
                        </ItemTemplate>
                        <EditItemTemplate>
                                <asp:RadioButtonList ID="LevelRBL" runat="server" RepeatDirection="Horizontal" AutoPostBack="true" AppendDataBoundItems="true">
                                    <asp:ListItem Value="0" Text="普通会员"></asp:ListItem>