yoast_seo_sitemap_include_empty_terms.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Include empty terms in the sitemap
 * Credit: Yoast team
 * Last Tested: Mar 22 2019 using Yoast SEO 10.0.1 on WordPress 5.1.1
 */
   
add_filter('wpseo_sitemap_exclude_empty_terms', '__return_false');