Tag Groups fix

function tg_add_taxonomy_columns( $columns )
{

    global $wp;

    $new_order = (isset( $_GET['order'] ) && $_GET['order'] == 'asc' && isset( $_GET['orderby'] ) && $_GET['orderby'] == 'term_group') ? 'desc' : 'asc';

    $screen = get_current_screen();

    if ( !empty( $screen )) {

        $taxonomy = $screen->taxonomy;

        $link = add_query_arg( array('orderby' => 'term_group', 'order' => $new_order, 'taxonomy' => $taxonomy), admin_url( "edit-tags.php" . $wp->request ) );

        $link_escaped = esc_url( $link );

        $columns['term_group'] = '<a href="' . $link_escaped . '"><span>' . __( 'Tag Group', 'tag-groups' ) . '</span><span class="sorting-indicator"></span></a>';

      }  else {

        $columns['term_group'] = '';

      }

    return $columns;

}