Merge pull request +10667 from c9/fix/dianose-flaky-w

Throw exception when e.theme is not valid to diagnose what's going on

package.json

@@ -114,6 +114,6 @@
         "c9.ide.threewaymerge": "#229382aa0b",
         "c9.ide.undo": "#b028bcb4d5",
         "c9.ide.upload": "#0bd010d3dc",
-        "c9.ide.welcome": "#336862828d"
+        "c9.ide.welcome": "#ab1740e33b"
     }
 }