Error :Object reference not set to an instance of an object

[HttpPost]

public ActionResult UserAccount(List items)

{

string Rolename = "";

int Roleid = 0;

string userid = "";

string updatedby = "";

string name = Request.Form["Txt_userid"].ToString(); //error linene please see view and controller //below

foreach (SelectListItem item in items)

{

if (item.Selected)

{

Rolename = item.Text;

Roleid = Convert.ToInt32(item.Value);

userid = "6090";

updatedby = "admin";

AIS.InsertRole_status(Roleid, 1, userid, updatedby);

}

else

{

Rolename = item.Text;

Roleid = Convert.ToInt32(item.Value);

userid = "6090";

updatedby = "admin";

AIS.InsertRole_status(Roleid, 0, userid, updatedby);

}

return View(items);

// UserAccount UA = new UserAccount();

// UA.SuperUsrChk = true;

// UA.RequestorUsrChk = false;

// // return View(new UserAccount { SuperUsrChk = true });

// return View(UA);

}

view

@model List

ViewBag.Title = "UserAccount";

}

@Scripts.Render("~/bundles/jquery")

@using (Html.BeginForm("UserAccount", "Admin"))

{

UserId

@for (int i = 0; i < Model.Count(); i++)

{

}

@Html.CheckBoxFor(m => m[i].Selected)	@Html.DisplayFor(m => m[i].Text) @Html.HiddenFor(m => m[i].Value) @Html.HiddenFor(m => m[i].Text)

}