The Color attributes for HTMLDocument should have [TreatNullAs=EmptyString]

Source/core/html/HTMLDocument.idl

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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 16 matching lines @@
     // Inheritance of [Unforgeable] attributes is not supported.  So we have to
     // define the same unforgeable attributes in derived interfaces as well.
     // See that Document already defined 'location' attribute and this interface
     // redefine it.
     // Keep all the definitions consistent.
     // TODO(yukishiino): Support inheritance of attributes defined on instance.
     [PutForwards=href, Unforgeable] readonly attribute Location? location;
 
     // https://html.spec.whatwg.org/#Document-partial
 
-    // FIXME: *Color should have [TreatNullAs=EmptyString].
-    [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString fgColor;
-    [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString linkColor;
-    [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString vlinkColor;
-    [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString alinkColor;
-    [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString bgColor;
+    [TreatNullAs=EmptyString, CustomElementCallbacks] attribute DOMString fgColor;
+    [TreatNullAs=EmptyString, CustomElementCallbacks] attribute DOMString linkColor;
+    [TreatNullAs=EmptyString, CustomElementCallbacks] attribute DOMString vlinkColor;
+    [TreatNullAs=EmptyString, CustomElementCallbacks] attribute DOMString alinkColor;
+    [TreatNullAs=EmptyString, CustomElementCallbacks] attribute DOMString bgColor;
 
     [MeasureAs=DocumentClear] void clear();
     [MeasureAs=DocumentCaptureEvents] void captureEvents();
     [MeasureAs=DocumentReleaseEvents] void releaseEvents();
 
     // FIXME: all should not be [Replaceable].
     [Replaceable, ImplementedAs=allForBinding] readonly attribute HTMLAllCollection all;
 };