[flexcoders] E4X descendent operator return type?

[tddclare]

I'm trying a simple test, and either it's monday or my brain is
broken... maybe both...

I'm writing a login component, and fire off a HTTP service that
returns XML as E4X.  The response XML is a <response> tag with either
a <user> tag or a <fault> tag inside of it.

All I want to do is test if there is a user or fault in the response!

I'm trying this:
private function handle(e:ResultEvent):void {
   if (e.result..user) {
      trace("Yippee!)
   }
   if (e.result..fault) {
      trace("Boo!)
   }
}

The event is firing, but I always get "Yippee" even when I point at a
file that has NO user tag.

I've replaced the conditional with everything I can think of:
e.result..user != null
e.result..user != ""

but it seems to fire no matter what.

If the E4X parser does NOT find the descendant, what does it return? 
Is this documented anywhere in the (not so good) Flex/AS3 documentation?

Thanks!

-- TC