wordpress查询数据库get_var不存在的记录，报致命错误，怎么设置只返回null而不报错

Question

// $rs = $wpdb->get_var($wpdb->prepare("SELECT * FROM $table WHERE number = $number"));

$rs = $wpdb->get_var($wpdb->prepare("SELECT count(*) FROM $table "));

报下面的错

Fatal error: Uncaught Error: Call to a member function get_var() on null in D:\phpStudy22\WWW\wordpress5.9\wp-content\themes\lsm2022\from.php:23 Stack trace: #0 {main} thrown in D:\phpStudy22\WWW\wordpress5.9\wp-content\themes\lsm2022\from.php on line 23