title: Unable to pre-set Radio button tied to null value
body: <p>I have a radio button:
  Options: [null,"N","U"], displaying [All, New, Used] on the ui.</p>
  
  <p>I can set the onAttach to widget.value = "N" or "U" and it works perfectly. If I set onAttach to widget.value = null, the UI has no selection.</p>
  
  <p>How can I force the first option, "All" to always be selected onAttach?</p>