The `getSent_date()` is sometimes null when the `getState()` is reported as `SENT`

The [`Message`](https://github.com/Syniverse/Messaging-Java/blob/master/scgapi/src/main/java/com/syniverse/scgapi/Message.java) returned by the call via `MessageRequest.Resource res = new MessageRequest.Resource(session);` has null value for `getSent_date()` even when the `getState()` is reported as `SENT`