Solve the problem of "search_by_title_only() expected to be a reference" on the website

Because of the PHP version, some of our friends may enable compatibility without reporting errors, so we can't see some problems. However, with the increase of logs, the server disk will be occupied. The PHP log prompts "search_by_title_only() expected to be a reference". How can I solve this problem?

 //PHP error reporting by laozuo.org add_filter('posts_search', 'laozuoorg_search_by_title_only', 500, 2); function laozuoorg_search_by_title_only($search) { global $wpdb, $wp_query; if (empty($search)) return $search; $q = $wp_query->query_vars; $n = ! empty($q['exact']) ? '' : '%'; $search = $searchand = ''; foreach ((array) $q['search_terms'] as $term) { $term = esc_sql($wpdb->esc_like($term)); $search .=  "{$searchand}($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')"; $searchand = ' AND '; } if (!empty($search)) { $search = " AND ({$search}) "; if (!is_user_logged_in()) $search .=  " AND ($wpdb->posts.post_password = '') "; } return $search; }