Cannot clear out multiselect #1139

As long as the user selects something in the multiselect, it works fine. But if the user de-selects all of the items in a multiselect, instead of clearing the selection, the selection remains unchanged.

I have a sample app demonstrating the problem in the empty-multiselect-bug branch on git://github.com/leedm777/lift-sample-app.git.

git clone git://github.com/leedm777/lift-sample-app.git -b empty-multiselect-bug

See related ML threads:
http://groups.google.com/group/liftweb/browse_thread/thread/9f8e460b8d57a741/eaa06d46106a134a
http://groups.google.com/group/liftweb/browse_thread/thread/e8c9fec7c3512fc7/91bba42ebcaa2941
http://groups.google.com/group/liftweb/browse_thread/thread/46e70d3130e52c18/8365d375163af9bb