Codeigniter 3 A PHP Error was encountered Severity: Warning Message: Undefined array key "id"

one text

i try to update or edit some data and ive got this error

here's my model

Jurusan_model.php

    private $table = "tbl_jurusan";
    public $id;
    public $jurusan;

    public function rules()
    {
        return [
            ['field' => 'jurusan',
            'label' => 'jurusan',
            'rules' => 'required']
        ];
    }

    public function update()
    {
        $post = $this->input->post();
        $this->id = $post["id"];
        $this->jurusan = $post["jurusan"];
        return $this->db->update($this->table, $this, array('id' => $post['id']));
    }

and the controller

JurusanController.php

    public function __construct()
    {
        parent::__construct();
        $this->load->model('Jurusan_model');
    }

    public function edit($id = null)
    {
        if (!isset($id)) redirect('JurusanController');

        $jurusan = $this->Jurusan_model;
        $validation = $this->form_validation;
        $validation->set_rules($jurusan->rules());

        if ($validation->run()) {
            $jurusan->update();
            redirect('JurusanController', $this->session->set_flashdata('success', 'Berhasil diubah'));
        }

        $data["jurusan"] = $jurusan->getJurusanById($id);
        if (!$data["jurusan"]) show_404();
        
        $this->load->view("edit/edit_jurusan", $data);
    }

and ive got this error

A PHP Error was encountered

Severity: Warning

Message: Undefined array key "id"

Filename: models/Jurusan_model.php

Line Number: 42

A PHP Error was encountered

Severity: Warning

Message: Undefined array key "id"

Filename: models/Jurusan_model.php

Line Number: 44

well i try

var_dump($jurusan);

at jurusan controller while i try update some data and here the result

object(Jurusan_model)#22 (3) { ["table":"Jurusan_model":private]=> string(11) "tbl_jurusan" ["id"]=> NULL ["jurusan"]=> string(10) "Tatabusana" }