map org.mozilla.javascript.Undefined to ruby nil

lib/rhino/wormhole.rb

@@ -1,9 +1,11 @@
 
 module Rhino
   module To        
+    JS_UNDEF = [J::Scriptable::NOT_FOUND, J::Undefined]
+    
     def ruby(object)
       case object
-      when J::Scriptable::NOT_FOUND then nil
+      when *JS_UNDEF      then nil
       when J::Wrapper     then object.unwrap
       when J::Scriptable  then NativeObject.new(object)
       else  object

spec/rhino/wormhole_spec.rb

@@ -33,6 +33,10 @@ describe Rhino::To do
         end
       end
     end
+    
+    it "converts javascript undefined into nil" do
+      To.ruby(J::Undefined.instance).should be_nil
+    end
   end
   
   describe  "javascript translation" do