returning null array in getting photos albums

<?php
$user_id = $facebook->require_login($required_permissions = 'email,photo_upload');
$has_permission = $facebook->api_client->users_hasAppPermission("photo_upload");
$albums=$facebook->ap开发者_C百科i_client->photos_getAlbums($user_id, NULL);
var_dump($albums);
?>

I am getting null when run this code

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Could you be more specific?

try to pass varialbe as a second argument