DateTime(Immutable) serialization doesn't work with php 7.4 RC1

[rybakit]

Code:

$data = new DateTimeImmutable();
var_dump(msgpack_unpack($packed = msgpack_pack($data)));
var_dump($packed);

Expected result:

class DateTimeImmutable#2 (3){
 public $date =>
 string(26) "2019-07-16 18:49:00.267050"
 public $timezone_type =>
 int(3)
 public $timezone =>
 string(3) "UTC"
}
string(80) "DateTimeImmutabledate2019-07-16 18:49:00.267050timezone_typetimezoneUTC"

Actual result:

object(DateTimeImmutable)#2 (0){
}
string(20) "DateTimeImmutable"

Versions:

$ php -v
PHP 7.4.0RC1 (cli) (built: Sep 5 2019 22:52:36) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0-dev, Copyright (c) Zend Technologies

$ php -r 'echo (new ReflectionExtension("msgpack"))->getVersion(), "\n";'
2.0.3