foreach ( $this->get_children( 'WPPTD\Components\Metabox' ) as $metabox ) {
                foreach ( $metabox->get_children() as $field ) {
                    $meta_value_old = wpptd_get_post_meta_value( $post_id, $field->slug );
                    if ( $meta_value_old === null ) {
                        $meta_value_old = $field->default;