Unable to locate session.php

Good day to All,

Currently, i am using CI 3.1.2.
There is an error like below.

"unable to locate the specified class: Session.php"

Below is my code. ci_sessions table also created.
Please help me if you guy already faced such error.

config.php

PHP Code:

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


autoload.php

PHP Code:

$autoload['libraries'] = array('session');