在asp.net中使用cookie时出现Nullpointerexception错误

我在if条件下得到nullpointerexception。如何解决此错误。我的代码和错误描述如下:

error: System类型的异常。NullReferenceException'在System.Web.dll中发生，但未在用户代码中处理

错误发生在这一行:if (Request.Cookies[name]。Value != null)

  public void SetCookie(string name, string value, int expiration)
    {
        HttpCookie cookie;
        cookie = new HttpCookie(name);
        if (Request.Cookies[name].Value != null)
        {
            DeleteCookie(name);
        }
        else
        {
            cookie.Value = value;
            cookie.Expires = DateTime.Now.AddDays(expiration);
            Response.Cookies.Add(cookie);
        }
    }

 public void SetCookie(string name, string value, int expiration)
{
    if(Request.Browser.Cookies)
    {
        if (Request.Cookies[name] != null)
        {
            DeleteCookie(name);
        }
        HttpCookie cookie;
        cookie = new HttpCookie(name);
        cookie.Value = value;
        cookie.Expires = DateTime.Now.AddDays(expiration);
        Response.Cookies.Add(cookie);
    }
}