Undefined index: isNewEntry

I have an error when a user save an existing entry as draft:

```
/craft/plugins/postmaster/core/parcel_types/DefaultParcelType.php(51)
Undefined index: isNewEntry
```

In $event->params, I have a "isNewDraft" but no "isNewEntry", but I'm not confortable enough to hack the code and test both variables ;) Should I?
