Make [TreatNullAs=NullString] DOMString arguments nullable instead

Source/core/dom/NamedNodeMap.idl

 /*
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 19 matching lines @@
 
     [RaisesException, CustomElementCallbacks, MeasureAs=NamedNodeMapRemoveNamedItem] Node removeNamedItem([Default=Undefined] optional DOMString name);
 
     [MeasureAs=NamedNodeMapItem] getter Node item([Default=Undefined] optional unsigned long index);
 
     readonly attribute unsigned long length;
 
 
     // Introduced in DOM Level 2:
 
-    [MeasureAs=NamedNodeMapGetNamedItemNS] Node getNamedItemNS([TreatNullAs=NullString, Default=Undefined] optional DOMString namespaceURI,
+    [MeasureAs=NamedNodeMapGetNamedItemNS] Node getNamedItemNS([Default=Undefined] optional DOMString? namespaceURI,
                                                                [Default=Undefined] optional DOMString localName);
 
     [RaisesException, CustomElementCallbacks, MeasureAs=NamedNodeMapSetNamedItemNS] Node setNamedItemNS([Default=Undefined] optional Node node);
 
-    [RaisesException, CustomElementCallbacks, MeasureAs=NamedNodeMapRemoveNamedItemNS] Node removeNamedItemNS([TreatNullAs=NullString, Default=Undefined] optional DOMString namespaceURI,
+    [RaisesException, CustomElementCallbacks, MeasureAs=NamedNodeMapRemoveNamedItemNS] Node removeNamedItemNS([Default=Undefined] optional DOMString? namespaceURI,
                                                                                                               [Default=Undefined] optional DOMString localName);
 
 };