Remove [TreatNullAs=NullString] from Document.domain

Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * 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 64 matching lines @@
     // FIXME: xmlEncoding/xmlVersion/xmlStandalone have been removed from the spec.
     [MeasureAs=DocumentXMLEncoding] readonly attribute DOMString? xmlEncoding;
     [RaisesException=Setter, MeasureAs=DocumentXMLVersion] attribute DOMString? xmlVersion;
     [RaisesException=Setter, MeasureAs=DocumentXMLStandalone] attribute boolean xmlStandalone;
 
     // HTML
     // https://html.spec.whatwg.org/#the-document-object
 
     // resource metadata management
     [PutForwards=href, Unforgeable] readonly attribute Location? location;
-    // FIXME: domain should not have [TreatNullAs=NullString].
-    [TreatNullAs=NullString, RaisesException=Setter] attribute DOMString domain;
+    [RaisesException=Setter] attribute DOMString domain;
     readonly attribute DOMString referrer;
     // FIXME: cookie should not have [TreatNullAs=NullString].
     [TreatNullAs=NullString, RaisesException] attribute DOMString cookie;
     readonly attribute DOMString lastModified;
     // FIXME: readyState should use the enum DocumentReadyState.
     // FIXME: readyState should not have [TreatReturnedNullStringAs=Undefined].
     [TreatReturnedNullStringAs=Undefined] readonly attribute DOMString readyState;
 
     // DOM tree accessors
     // FIXME: title and dir should not have [TreatNullAs=NullString].
@@ skipping 121 matching lines @@
     attribute EventHandler onsearch;
     [RuntimeEnabled=ExperimentalContentSecurityPolicyFeatures] attribute EventHandler onsecuritypolicyviolation;
     attribute EventHandler onselectionchange;
     attribute EventHandler onselectstart;
     attribute EventHandler onwheel;
 };
 
 Document implements GlobalEventHandlers;
 Document implements ParentNode;
 Document implements NonElementParentNode;