Make [TreatNullAs=NullString] DOMString arguments nullable instead

Source/core/dom/Element.idl

Index: Source/core/dom/Element.idl
diff --git a/Source/core/dom/Element.idl b/Source/core/dom/Element.idl
index 7593e26bfe8ba3111406ae4d388ea9257ff68645..5416124143a7a0bf2ea0825c138f4ffa6dcba0ef 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -39,15 +39,15 @@
 
     // DOM Level 2 Core
 
-    DOMString? getAttributeNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString localName);
-    [RaisesException, CustomElementCallbacks] void setAttributeNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString qualifiedName, DOMString value);
-    [CustomElementCallbacks] void removeAttributeNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString localName);
-    HTMLCollection getElementsByTagNameNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString localName);
-    [MeasureAs=ElementGetAttributeNodeNS] Attr getAttributeNodeNS([TreatNullAs=NullString, Default=Undefined] optional DOMString namespaceURI,
+    DOMString? getAttributeNS(DOMString? namespaceURI, DOMString localName);
+    [RaisesException, CustomElementCallbacks] void setAttributeNS(DOMString? namespaceURI, DOMString qualifiedName, DOMString value);
+    [CustomElementCallbacks] void removeAttributeNS(DOMString? namespaceURI, DOMString localName);
+    HTMLCollection getElementsByTagNameNS(DOMString? namespaceURI, DOMString localName);
+    [MeasureAs=ElementGetAttributeNodeNS] Attr getAttributeNodeNS([Default=Undefined] optional DOMString? namespaceURI,
                                                                   [Default=Undefined] optional DOMString localName); // Removed from DOM4.
     [RaisesException, CustomElementCallbacks, DeprecateAs=ElementSetAttributeNodeNS] Attr setAttributeNodeNS([Default=Undefined] optional Attr newAttr); // Removed from DOM4.
     boolean hasAttribute(DOMString name);
-    boolean hasAttributeNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString localName);
+    boolean hasAttributeNS(DOMString? namespaceURI, DOMString localName);
 
     [PerWorldBindings] readonly attribute CSSStyleDeclaration style;