Add 'position-filled' body class on filled single listings

gistfile1.txt

add_filter( 'body_class', 'dj_add_position_filled_class' );

function dj_add_position_filled_class( $classes ) {
    global $post;
    if ( $post->post_type !== 'job_listing' ) {
        return $classes;
    }
    if ( is_position_filled( $post ) ) {
        $classes[] = 'position-filled';
    }
    return $classes;
}