Invalid serialization data for DateTime object

Hi,

I create an entity and cache it. When I try to get from cache it gives me error: "Invalid serialization data for DateTime object".

This is example code:

Code:

$web = new \App\Entities\Web();
$web->created_at = date('Y-m-d H:i:s');
$cache->save('webname', $web, 300);

$web = $cache->get('webname');
if ($web) {
    echo 'cached';
    printr($web);
}

Where is the problem? How can fix this?

Thank you,

Angel