public function __construct($instagram, $mediaId, $caption = null)
{
parent::__construct($instagram);
$this->mediaId = $mediaId;
$caption = $caption != null ? $caption : "";
$this->setSignedBody(array("caption_text" => $caption, "_csrftoken" => $instagram->getCSRFToken(), "usertags" => json_encode(array("in" => array())), "_uid" => $instagram->getLoggedInUser()->getPk(), "_uuid" => $instagram->getUUID(), "location" => "{}"));
}