private URL _getPictureURL(String objectId, PictureSize size) throws FacebookException {
        String url = buildEndpoint(objectId, "picture");
        HttpResponse res;
        if (size != null) {
            res = get(url, new HttpParameter[]{new HttpParameter("type", size.toString())});
        } else {
            res = get(url);
        }
        try {
            return new URL(res.getResponseHeader("Location"));
        } catch (MalformedURLException urle) {
            throw new FacebookException(urle.getMessage(), urle);
        }
    }