There isn't sufficient testing for the handling of null OpaqueJSStrings. This is evident from the changes to OpaqueJSString in r130344 from https://bugs.webkit.org/show_bug.cgi?id=98300 and its follow-ons.
Created attachment 167824 [details] Patch
Comment on attachment 167824 [details] Patch r=me
Comment on attachment 167824 [details] Patch Clearing flags on attachment: 167824 Committed r130832: <http://trac.webkit.org/changeset/130832>
All reviewed patches have been landed. Closing bug.