Created Unassigned: UserMentions are null with Tweet with photo [2549]

Consider the following code:

```
//Tweet 499237584485486593:
//@SwiftKey you guys make the best keyboard! Rocks both my devices.
//I think Taylor should consider changing her name http://t.co/NCRN37b4oj

var tweet = Tweet.GetTweet(499237584485486593);

if (tweet.UserMentions == null || tweet.UserMentions.Count != 1)
{
throw new Exception("We have a problem. UserMentions are not okay.");
}
```

When I use a photo (might be a link), the UserMention collection remains null. It should have 1: "@SwiftKey". I've encountered this behavior also when I'm reading the tweet from a timeline.