getLicenses() in UsageStream returns null in Usage API but content is in response data

[fathlon]

DataSiftClient dataSiftClient = new DataSiftClient(new DataSiftConfig("xxx", "xxx"));
Usage usage = dataSiftClient.usage(Period.HOUR).sync();
UsageStream stream = usage.getStreams();

System.out.println(usage.getResponse().data());
Returns:
{"start":"Thu, 27 Aug 2015 08:50:00 +0000","end":"Thu, 27 Aug 2015 09:50:00 +0000","streams":{"1bb086ff4f9d58cca88a1cb706968652":{"licenses":[],"seconds":3600},"293e675770333ca7696da411109633d6":{"licenses":[],"seconds":3600},"2f8540ed0f2056bd6b0db4cba7eceff5":{"licenses":
... ... ..

System.out.println(stream.getLicenses());
Returns:
null

Seems like the response data is not set into UsageStream, or is it something I missed out?