Do not special case null for URLUtils attributes

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

 description('Test setting the hash attribute of the URL in HTMLAnchorElement.');
 
 var a = document.createElement('a');
 
 debug("Hash value does not start with '#'");
 a.href = "https://www.mydomain.com:8080/path/testurl.html#middle";
 a.hash = "hash-value";
 shouldBe("a.href", "'https://www.mydomain.com:8080/path/testurl.html#hash-value'");
 
 debug("Hash value starts with '#'");
 a.href = "file:///path/testurl.html#middle";
 a.hash = "#hash_value";
 shouldBe("a.href", "'file:///path/testurl.html#hash_value'");
 
 debug("'?' in hash value");
 a.href = "http://www.mydomain.com/path/testurl.html#middle";
 a.hash = "#hash?value";
 shouldBe("a.href", "'http://www.mydomain.com/path/testurl.html#hash?value'");
 
 // The expected behavior should change when character table is updated.
 // IE8 and Firefox3.5.2 don't consider these characters as illegal.
 debug("'#' in hash value, and illegal characters in hostname");
 a.href = "https://www.my\"d(){}|~om?ain#com/path/testurl.html#middle";
 a.hash = "#hash#value";
 shouldBe("a.href", "'https://www.my\"d(){}|~om?ain#com/path/testurl.html#middle'");
 
-// IE8 converts null to "null", which is not the right thing to do.
-// Firefox 3.5.2 removes the '#' at the end, and it should per
-// http://dev.w3.org/html5/spec/infrastructure.html#url-decomposition-idl-attributes .
 debug("Set hash to null");
 a.href = "https://www.mydomain.com/path/testurl.html#middle";
 a.hash = null;
-shouldBe("a.href", "'https://www.mydomain.com/path/testurl.html#'");
+shouldBe("a.href", "'https://www.mydomain.com/path/testurl.html#null'");
 
 // Firefox 3.5.2 removes the '#' at the end, and it should per
 // http://dev.w3.org/html5/spec/infrastructure.html#url-decomposition-idl-attributes .
 debug("Set hash to empty string");
 a.href = "https://www.mydomain.com/path/testurl.html#middle";
 a.hash = "";
 shouldBe("a.href", "'https://www.mydomain.com/path/testurl.html#'");
 
 // Firefox 3.5.2 does not allow setting hash to mailto: scheme, and it should.
 debug("Add hash to mailto: protocol");
@@ skipping 15 matching lines @@
 
 // Firefox 3.5.2 does not allow setting hash to foo: scheme, and it should.
 debug("Add hash to non-standard protocol");
 try {
 a.href = "foo:bar";
 a.hash = "#hash";
 shouldBe("a.href", "'foo:bar#hash'");
 } catch(e) {
 debug("Exception: " + e.description);
 }