Fix sending private-message in hipchat

When I run `private-message` on an actual hipchat connection, I get:

```clojure
paraseba.eliga.bot=> (private-message hipchat mybot "nicoberger@gmail.com" "hola")

NullPointerException null keys not allowed  org.jivesoftware.smack.util.collections.AbstractReferenceMap.put (AbstractReferenceMap.java:249)
```

I'm looking into it.