Unlike WKStringRefs, we should allow returning null WKURLRefs as the concept of an empty URL makes little sense.
Created attachment 72215 [details] Patch
<rdar://problem/8575621>
Landed in r70795.
http://trac.webkit.org/changeset/70795 might have broken Qt Linux Release The following tests are not passing: fast/dom/Window/window-property-descriptors.html