public PopularPhotoCollection StatsGetPopularPhotos(DateTime? date, PopularitySort sort, int page, int perPage)
 {
     var dictionary = new Dictionary<string, string>();
     dictionary.Add("method", "flickr.stats.getPopularPhotos");
     if (date != null) dictionary.Add("date", date.Value.ToUnixTimestamp());
     if (sort != PopularitySort.None) dictionary.Add("sort", sort.ToString().ToLower());
     if (page != 0) dictionary.Add("page", page.ToString(CultureInfo.InvariantCulture));
     if (perPage != 0) dictionary.Add("per_page", perPage.ToString(CultureInfo.InvariantCulture));
     return GetResponse<PopularPhotoCollection>(dictionary);
 }