function asArray()
{
return array_merge(parent::asArray(), array_filter($this->linkDict));
}
/**
* Add a link to the JSON document
*
* @param string $url the URL for the link
* @param string $rel the link relationship
*/
function addLink($url = null, $rel = null, $mediaType = null)
{
$link = new ActivityStreamsLink($url, $rel, $mediaType);
array_push($this->links, $link->asArray());
}