Make [TreatNullAs=NullString] DOMString arguments nullable instead

Source/core/dom/NamedNodeMap.idl

Index: Source/core/dom/NamedNodeMap.idl
diff --git a/Source/core/dom/NamedNodeMap.idl b/Source/core/dom/NamedNodeMap.idl
index 7de6a6f8454c01016c2b44773fcb0f4d52dc38e7..62944049120990845f4c5f38c13cf2dbdb2783b6 100644
--- a/Source/core/dom/NamedNodeMap.idl
+++ b/Source/core/dom/NamedNodeMap.idl
@@ -37,12 +37,12 @@
 
     // 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);
 
 };