add body class if current user is subscriber

add_class_if_subscriber

add_filter( 'body_class', 'add_class_if_subscriber' );
function add_class_if_subscriber( $classes ) {

    $user_ID = get_current_user_id();
    $subscriber = mailster('subscribers')->get_by_wpid($user_ID);
    if($subscriber){
        $classes[] = 'is-mailster-subscriber';
    }
    return $classes;
}