getNextId() += 0 ?

https://github.com/jchadwick/EssentialTypeScriptBook/blob/master/manuscript/05.Classes.md

``` ts
TodoService.getNextId = function() {
    return TodoService.lastId += 0;
}
```

Is `+= 0` intentional? I assume you meant `+= 1`? If not then I'm unclear why it would need to have the `+= 0`.
