adding a site Login/Logout

Hi
I tried adding a site Login/Logout link to my primary menu with this:

function add_login_logout_link( $items, $args  ) {
	if( $args->theme_location == 'primary' ) {
	        $loginoutlink = wp_loginout('index.php', false);
	        $items .= '<li">'. $loginoutlink .'</li>';
			return $items;
	    }
	    return $items;
}
add_filter( 'wp_nav_menu_items', 'add_login_logout_link', 10, 2 );

It didn’t work. Can you help me?