[Resolved]Session Error of non-object for login controller

[eluser][email protected][/eluser]
login.php

Code:

class login extends CI_Controller {

public function __construct()
{
  parent::__construct();
  $this->load->database();
  $this->load->model('login_model');
}//__construct() END

public function index() {
  $data['main_content']='login-form';
  $this->load->view('include/template', $data);
}//index() END

public function validate_credentials() {
  $this->load->model('login_model');
  $query = $this->login_model->validate();
  
  if($query){ // if user cred. valid then...
   $data = array(
    'mem_username'=>$this->input->post('mem_username'),
    'mem_logged_in'=>true
   );
  
   $this->session->set_userdata($data);
   redirect('user_area');
  } else {
   $this->index();
   echo 'Invalid Account!';
  
  }
}

Hello, my login.php controller always get returned on the line $this->session->set_userdata($data);
The message says:
A PHP Error was encountered

Severity: Notice

Message: Undefined property: login::$session

Filename: controllers/login.php

Line Number: 26

Could anyone tell me why it says my $query is undefined? its not empty array when running btw, since it passed the validate().

Thank you

[eluser][email protected][/eluser]
Resolved, but why I need to add below code when I already added the session library to the autoload.php?

Code:

class login extends CI_Controller {

public function __construct()
{
  parent::__construct();
  $this->load->database();
  $this->load->library('session');
  $this->load->model('login_model');
}//__construct() END

Resolved....was incorrectly loaded into package instead of library lol