AngularFire $createUser 's promise doesn't return an object containing user data

According to the documentation the $createUser function, "... returns a promise that is resolved with an object containing user data about the created user"

http://ift.tt/1HUYS9m

When I use the function (see code below), I can register the user sucessfully but when I read the variable that should contain the UID, it's not defined.

In Chrome's console I get: "TypeError: Cannot read property 'uid' of undefined"

Am I doing something wrong? Should I be retrieving the value differently?

myApp.factory('Authentication', function($firebase, $firebaseAuth, FIREBASE_URL, $location, $rootScope) {
// using $firebaseAuth instead of SimpleLogin 

var ref = new Firebase(FIREBASE_URL);
var authObj = $firebaseAuth(ref);

var myObject = {
    login : function(user) {
        console.log('authentication.js: logging in')
        return authObj.$authWithPassword({
            email: user.email,
            password: user.password
        });
    }, //login

    logout : function(){
        return authObj.$unauth();
    }, // logout 

    register : function(user) {
        console.log('authentication.js: registering user')
        return authObj.$createUser({
            email: user.email,
            password: user.password
        }).then( function(userData) {
            console.log("User " + userData.uid + " created successfully!");
        });
    } // register

} //myObject

return myObject;
});