No, of course I don't want to extend XMPP in such a bad way. But I've already seen <iq type="ERROR"/> (upper case), which either came from an older Smack version, or maybe from ejabberd, I can't remember/know exactly.
If you would convert this to an enum e.g. using Enum.valueOf it would throw an IllegalArgumentException, very similar to the exception on a wrong date.
I was curisous, if the connection is closed in that case, too, or how do you deal with it?
Btw, your link about extending in the wrong way is hilarious :-D :-D
