A working sort for taxonomy terms + numeric meta data

functions::taxonomies.php

<?php
register_taxonomy( 'uh_service_type_taxonomy', array( 'contact_cpt' ), $args );

    // add and 'Order' column to Service Type taxonomy terms
    add_filter("manage_edit-uh_service_type_taxonomy_columns", "on_manage_edit_uh_service_type_taxonomy_columns");
    function on_manage_edit_uh_service_type_taxonomy_columns( $columns ) {
      $columns['term_order'] = __('Order');
      return $columns;
    }

    // Output the term's sort order
    add_filter( 'manage_uh_service_type_taxonomy_custom_column', 'on_manage_uh_service_type_taxonomy_custom_column', 10, 3);
    function on_manage_uh_service_type_taxonomy_custom_column($out, $column_name, $term_id) {
      switch ($column_name) {
        case 'term_order':
          $out = get_field('taxonomy_term_order', get_term($term_id));
          break;
        default:
          break;
      }
      return $out;
    }

    add_filter( 'manage_edit-uh_service_type_taxonomy_sortable_columns', 'uh_service_type_taxonomy__sortable' );
    function uh_service_type_taxonomy__sortable( $columns ) {
        $columns['term_order'] = 'term_order';
        return $columns;
    }

    // Finally. A working sort for taxonomy terms + numeric meta data
    add_filter('pre_get_terms', 'uh_service_type_taxonomy__orderby');
    function uh_service_type_taxonomy__orderby( $term_query ) {
      global $pagenow;
      if(!is_admin()) {
        return $term_query;
      }
      // WP_Term_Query does not define a get() or a set() method so the query_vars member must
      // be manipulated directly
      if(is_admin() && $pagenow == 'edit-tags.php' && $term_query->query_vars['taxonomy'][0] == 'uh_service_type_taxonomy' && (!isset($_GET['orderby']) || $_GET['orderby'] == 'term_order')) {
        // set orderby to the named clause in the meta_query
        $term_query->query_vars['orderby'] = 'order_clause';
        $term_query->query_vars['order'] = isset($_GET['order']) ? $_GET['order'] : "DESC";
        // the OR relation and the NOT EXISTS clause allow for terms without a meta_value at all
        $args = array('relation' => 'OR',
          'order_clause' => array(
            'key' => 'taxonomy_term_order',
            'type' => 'NUMERIC'
          ),
          array(
            'key' => 'taxonomy_term_order',
            'compare' => 'NOT EXISTS'
          )
        );
        $term_query->meta_query = new WP_Meta_Query( $args );
      }
      return $term_query;
    }