I have a custom endpoint where I want to change HTTP response status to 404 in certain scenarios (e.g post does not exist). How can I do that? Here is an example of custom endpoint:

```
function af_news_single( \WP_REST_Request $data ) {
    global $wpdb;

    $year = (int) $data['year'];
    $month = (int) $data['month'];
    $day = (int) $data['day'];
    $slug = $data['slug'];

    $date = "{$year}-{$month}-{$day}";

    $news = $wpdb->get_row(
        $wpdb->prepare(
            "SELECT
                DATE_FORMAT(post_date, %s) as `post_date`,
                `post_title`,
                `post_name`,
                `post_content`
             FROM {$wpdb->posts}
             WHERE
                `post_status` = 'publish' AND
                `post_type` = 'post' AND
                `post_name` = %s AND
                `post_date` BETWEEN %s AND %s + INTERVAL 1 DAY
             LIMIT 1
             ", '%Y-%m-%dT%TZ', $slug, $date, $date
        )
    );

    if ( $news ) {
        $news->post_title = qtranxf_translate( $news->post_title );
        $news->post_content = wpautop( qtranxf_translate( $news->post_content ) );
    } else { /* How to change response code? */ }

    return [ 'data' => $news ];
}

```

How can I change response code in this function?