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

Source/core/html/HTMLDocument.idl

Index: Source/core/html/HTMLDocument.idl
diff --git a/Source/core/html/HTMLDocument.idl b/Source/core/html/HTMLDocument.idl
index daa8c685cb9e25a059ffeaa53127b91c63f57583..d8360771dd1565cd3fa30b5c93b2c110391ff6b1 100644
--- a/Source/core/html/HTMLDocument.idl
+++ b/Source/core/html/HTMLDocument.idl
@@ -34,12 +34,11 @@ interface HTMLDocument : Document {
 
     // 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();