Doctrine ODM : PersistentCollection::toArray returns empty array - php

Question

Here's a definition of the field for the main document:
/**
* #var ArrayCollection
* #MongoDB\ReferenceMany(
* targetDocument="Some\Namespace\Document\Reference",
* sort={"creationDate": "desc"},
* simple=true
* )
* #Expose
* #Groups({"Main"})
* #Type("ArrayCollection<Some\Namespace\Document\Reference>")
* #var \Some\Namespace\Document\Reference[]
*/
protected $references;
I tried to get a list of main documents and serialized them via JMS Serializer, but I found, that references is empty array. After some investigation, I discovered, that for getReferences, documents returns instance of PersistentCollection for which:
count returns 2 [ok]
getMongoData returns array of MongoIds [ok]
toArray returns empty array [invalid]
Looks like that's because of initialize method, that clears mongoData.
I achived the proper outcome with following code:
/**
* #VirtualProperty
* #SerializedName("reference_ids")
* #Groups("Main")
* #return array
*/
public function getReferenceIds()
{
$out = array();
foreach ($this->getReferences()->getMongoData() as $val) {
$out[] = (string)$val;
}
return $out;
}
But it's only a shortcut and I don't feel, that's a proper solution.
If anyone has an idea how to retrieve these ids or whole documents using PersistentCollection and why initialize method clears mongoData ?
Thanks.