Do not special case null for URLUtils attributes

LayoutTests/fast/dom/HTMLAnchorElement/script-tests/set-href-attribute-search.js

 description('Test setting the search attribute of the URL in HTMLAnchorElement .');
 
 var a = document.createElement('a');
 
 debug("Set search without '?'");
 a.href = "https://www.mydomain.com/path/?key=value";
 a.search = "value=key";
 shouldBe("a.href", "'https://www.mydomain.com/path/?value=key'");
 
 // IE8 does not encode spaces in search string
@@ skipping 15 matching lines @@
 shouldBe("a.href", "'https://www.mydomain.com/path/?value%23key#hash'");
 } catch(e) {
 debug("Exception: " + e.description);
 }
 
 debug("Set search to a malformed URL");
 a.href = "bad:/|/url";
 a.search = "?value=key";
 shouldBe("a.href", "'bad:/|/url?value=key'");
 
-// IE8 converts null to "null", which is not the right thing to do.
 debug("Set search to null");
 a.href = "https://www.mydomain.com/path/?key=value";
 a.search = null;
-shouldBe("a.href", "'https://www.mydomain.com/path/'");
+shouldBe("a.href", "'https://www.mydomain.com/path/?null'");
 
 // Firefox 3.5.2 Removes the '?', and it shouldn't, per
 // http://dev.w3.org/html5/spec/infrastructure.html#url-decomposition-idl-attributes .
 debug("Set search to empty string");
 a.href = "https://www.mydomain.com/path/?key=value";
 a.search = "";
 shouldBe("a.href", "'https://www.mydomain.com/path/?'");