My stack : symfony 6.4 and php8.1

I encountered a problem when i want to use cache in symfony with the save method like below.

    $item = $cache->getItem('my_cache_key');
    if (!$item->isHit()) {

        $item->set('new_value1');
        $item->expiresAfter(3600);

        $cache->save($item);

    }

The result is :

SymfonyComponentCacheCacheItem {#1105 ▼
  #key: "my_cache_key"
  #value: "new_value1"
  #isHit: false
  #expiry: 1718978664.0953
  #metadata: []
  #newMetadata: []
  #innerItem: null
  #poolHash: null
  #isTaggable: false
}

Then, when i want to retrieve information from cache the field expiry is empty

    $item = $cache->getItem('my_cache_key');
    echo "<br/>object";
    dump($item);

The result is :

SymfonyComponentCacheCacheItem {#1115 ▼
  #key: "my_cache_key"
  #value: "new_value1"
  #isHit: true
  #expiry: null
  #metadata: []
  #newMetadata: []
  #innerItem: null
  #poolHash: null
  #isTaggable: false
}

Any ideas ?

I expected yo find the date expiry after having hit the cache