Undefined variable dan Column cannot be null pada codeigniter

Bantuanya temen", aku yang masih newbie banget ada tugas suruh perbaikin web, baru pertama pake CI, udah lari kesana kemari belom dapet jawabannya hehe.

-Controller

 function konfirmasi($id,$jumlah){
         if($this->session->userdata("username") == null) redirect("login/index");
        date_default_timezone_set("Asia/Jakarta");
        $time = Date('Y-m-d');
        $where = array(
            'id_topup' => $id,
            );
        $user = $this->m_customer->getUser("saldo_topup",$where)->row();
        $view['saldo'] = $this->m_customer->get_saldoAkhir($user->id_user);
        foreach($view['saldo']->result_array() as $row){
            $kartu = $row['id_kartu'];
            $saldo= $row['saldo'];
        }
        $info = array(
                    'id_kartu' => $kartu,
                    'saldo_awal' => $saldo,
                    'saldo_up' => $jumlah,
                    'saldo_akhir' => $saldo + $jumlah,
                    'keterangan'  => 'TOPUP SALDO',
                    'date' => $time
            );
        $this->m_customer->update_saldo($kartu,$jumlah,$id);
        $this->db->insert('kartu_history', $info);

        redirect('customer/saldo');
    }

-Model

 function getUser($table,$id){
        return $this->db->get_where($table,$id);
    }
    function get_saldo(){

        $query=$this->db->query("select username,nama_customer,tgl_topup,jumlah, s.status, ket, bank, bukti, id_topup from saldo_topup s join user u on u.id_user=s.id_user");
        return $query;

    }
    function get_saldoAkhir($id){

        $query=$this->db->query("select * from kartu where id_user = $id");
        return $query;

    }

- Errornya