我已将此代码设置为管理wordpress中帖子页面列表中的过滤器。如果所有变量都不为null，则运行此筛选器，如下所示：？类型=公寓和；面积=基安蒂；价格=A

但当其中一个为空时，代码会给我一个空结果。我如何修复？

if(isset($type_search) OR isset($area_search)  OR isset($prezzo_search)) {
    $posts = get_posts(array(
        \'posts_per_page\'    => -1,
        \'meta_query\'    => array(
            \'relation\'      => \'AND\',
            array(
                \'relation\' => \'AND\',
                array(
                    \'key\'       => \'villa_type_buy\',
                    \'value\'     => $type_search,
                    \'compare\'   => \'=\'
                ),
                array(
                    \'key\'       => \'Area\',
                    \'value\'     => $area_search,
                    \'compare\'   => \'=\'
                )
            ),
            array(
                \'key\'       => \'price_buy\',
                \'value\'     => array( $start_price, $end_price ),
                \'type\' => \'numeric\',
                \'compare\'   => \'BETWEEN\'
            )
        )
    ));
}