Default group property for FxRadioButton is [Object FxRadioButtonGroup] not "undefined"

Steps to reproduce:
1. Compile & run:
<?xml version="1.0" encoding="utf-8"?>
<FxApplication
xmlns="http://ns.adobe.com/mxml/2009" xmlns:local="*"
backgroundColor="0xFFFFFF" >
<layout><VerticalLayout/></layout>
<FxRadioButton id="s1" label="Spark 1" />
<Label text="

"/>
</FxApplication>

Actual Results:
Returns [Object FxRadioButtonGroup]

Expected Results:
Either docs should say that group defaults to "radioGroup" like groupName does or it should return undefined.

Workaround (if any):