get withExpiration does not return expiration

<?php

$connectionString = "couchbase://localhost?fetch_mutation_tokens=1";$cluster = new \Couchbase\Cluster($connectionString);

$cluster->authenticateAs("Administrator", "password");

$bucket = $cluster->bucket("travel-sample");

$collection = $bucket->defaultCollection();

$opts = new \Couchbase\UpsertOptions();$upsertResult = $collection->upsert("foo", "bar", $opts->expiration(10));

$options = new \Couchbase\GetOptions();$getResult = $collection->get("foo", $options->withExpiration(true));

var_dump($getResult->expiration());