getting error "object refrence not set to an instance of an objest

DataBaseClass dbClass = new DataBaseClass();
       public DataTable dt;
       protected void Page_Load(object sender, EventArgs e)
       {
           if (!Page.IsPostBack)
           {
               GetUserScraps(int.Parse(Request.QueryString["id"].ToString()));//here i've met error..

           }
       }

       public void GetUserScraps(int id)
       {
           string getUserScraps = "SELECT r.uid ,r.unm,p.photo,s.uid,s.unm,s.text,s.date,s.sid FROM register as r, status as s, profile as p WHERE   p.pid.s.sid AND r.email=p.email AND s.unm='" + Request.QueryString["id"].ToString() + "'";
           dt = dbClass.ConnectDataBaseReturnDT(getUserScraps);
           if (dt.Rows.Count > 0)
           {
               GridViewUserScraps.DataSource = dt;
               GridViewUserScraps.DataBind();
           }
       }