Codeigniter Database Error : 1064 Using MySQL and maybe some session config error

I'm currently using Codeigniter 3.xx and I trying to make a multilevel login using session checking. I got some tutorial from another website, but there's an error with query. By the way this is for the controler :

    <?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Auth extends CI_Controller {

    public function index() {
        $this->load->view('login');
    }

    public function cek_login() {
        $data = array('nip' => $this->input->post('nip'),
                        'password' => $this->input->post('password')
            );
        $this->load->model('user_m'); 
        $hasil = $this->user_m->cek_user($data);
        if ($hasil->num_rows() == 1) {
            foreach ($hasil->result() as $sess) {
                $sess_data['logged_in'] = 'Sudah Loggin';
                $sess_data['nip'] = $sess->nip;
                $sess_data['akses'] = $sess->akses;
                $this->session->set_userdata($sess_data);
            }
            if ($this->session->userdata('akses')=='admin') {
                redirect('admin');
            }
            elseif ($this->session->userdata('akses')=='member') {
                redirect('user');
            }       
        }
        else {
            echo "<script>alert('Gagal login: Cek username, password!');history.go(-1);</script>";
        }
    }

}

?>

This is the model for the controller :

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

    class User_m extends CI_Model {

        public function cek_user($data) {
            $query = $this->db->get_where(`pegawai`, $data);
            return $query;
        }

    }

?>

Then I got this error :

Error Number: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'WHERE nip = '21212121' AND password = 'user'' at line 2 SELECT * WHERE nip = '21212121' AND password = 'user' Filename: C:/xampp/htdocs/simpeg/application/models/User_m.php Line Number: 7

The things that I know I don't use MariaDB Engine for this table, and it should be logged in as user if that run correctly. Can anybody explain what was the wrong with this syntax? By the way I'm using newest XAMPP for PHP 7 and Codeigniter in this project

UPDATE After I tried some code, I thought that I have some problem with the session configuration. This is my config.php for session:

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

And this is my configuration in Session.php in system folder :

class CI_Session {

    var $sess_encrypt_cookie        = FALSE;
    var $sess_use_database          = FALSE;
    var $sess_table_name            = '';
    var $sess_expiration            = 7200;
    var $sess_expire_on_close       = FALSE;
    var $sess_match_ip              = FALSE;
    var $sess_match_useragent       = TRUE;
    var $sess_cookie_name           = 'ci_session';
    var $cookie_prefix              = '';
    var $cookie_path                = '';
    var $cookie_domain              = '';
    var $cookie_secure              = FALSE;
    var $sess_time_to_update        = 300;
    var $encryption_key             = '';
    var $flashdata_key              = 'flash';
    var $time_reference             = 'time';
    var $gc_probability             = 5;
    var $userdata                   = array();
    var $CI;
    var $now;

In the new version of Codeigniter (which one I use), whenever I tried to autoload session there always asked me to put some encryption key for the session, so after I put the encryption key there's an error in the query about session like this: Error Number: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'SET last_activity = 1455761673, user_data = 'a:2:{s:9:\"user_data\";s:0:\"\"' at line 1 UPDATE SET last_activity = 1455761673, user_data = 'a:2:{s:9:\"user_data\";s:0:\"\";s:3:\"nip\";s:10:\"1234567890\";}' WHERE session_id = '316bdf2f67b16beafbe30b56bca3833d' Filename: libraries/Session.php Line Number: 306