Esclude old post from sitemap: works but sitemap index display the sitemap blank

Hi all,

I want to exclude all post older then the last 2 years in my YOAST sitemap.
I use the wpseo_exclude_from_sitemap_by_post_ids filter to do that.

function exclude_posts_from_xml_sitemaps()
{
  global $wpdb;
  /*$date = new DateTime('first day of this year');
  $date_str = $date->format('Y-m-d H:i:s');*/
  $date_str =  '2018-01-31 00:00:00';
  $query = " SELECT ID FROM $wpdb->posts WHERE post_date < '$date_str' AND post_type   = 'post' ORDER BY post_date DESC";
  $results = $wpdb->get_results($query);
  foreach ($results as $result) {
    $array[] = $result->ID;
  }
  return $array;
}

add_filter('wpseo_exclude_from_sitemap_by_post_ids', 'exclude_posts_from_xml_sitemaps');

All works fine but sitemap_index.xml still display some (empty) post-sitemap1.xml post-sitemap2.xm etc.

Seems like the main sitemap not check if content of related sub post-sitemap is greater then 0 before add it.

Some suggestion?