Add regression test.

git-svn-id: svn://10.0.0.236/trunk@247326 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/js/rhino/testsrc/jstests/420012.jstest

@@ -0,0 +1,19 @@
+var o = new Object;
+o.setX = function (id) {
+  this.oid = id;
+}
+
+function setX(n) {
+  if (n == "" || n == null)
+    n = 0;
+
+  var s = new Object;
+  s.xyz = n;
+
+  if (s != null) {
+    o.setX(s.xyz);
+  }
+}
+
+setX('x');
+"success";