How to validate an optional field? about validator HOT 4 CLOSED

public function rules(): array
{
    return [
        'recipient' => [empty($this->getAttributeValue('recipient')) ? new Callback(function () {
            $result = new Result();
            return $result;
        }) : (new Email())->checkDNS(true)->enableIDN(true)],
    ];
}

public function rules(): array
{
    return [
        'recipient' => new Email())->checkDNS(true)->enableIDN(true)->skipOnEmpty(true),
    ];
}