/**
  * Set the alternative labels.
  *
  * @since 3.2.0
  *
  * @param int $post_id The post id.
  * @param array $alt_labels An array of labels.
  */
 public function set_alternative_labels($post_id, $alt_labels)
 {
     // Force $alt_labels to be an array
     if (!is_array($alt_labels)) {
         $alt_labels = array($alt_labels);
     }
     $this->log_service->debug("Setting alternative labels [ post id :: {$post_id} ][ alt labels :: " . implode(',', $alt_labels) . " ]");
     // Delete all the existing alternate labels.
     delete_post_meta($post_id, self::ALTERNATIVE_LABEL_META_KEY);
     // Set the alternative labels.
     foreach ($alt_labels as $alt_label) {
         if (!empty($alt_label)) {
             add_post_meta($post_id, self::ALTERNATIVE_LABEL_META_KEY, $alt_label);
         }
     }
 }