XMLSerializer.serializeToString() should throw exception for invalid node value.

Source/core/xml/XMLSerializer.cpp

Index: Source/core/xml/XMLSerializer.cpp
diff --git a/Source/core/xml/XMLSerializer.cpp b/Source/core/xml/XMLSerializer.cpp
index 74be0eac04d0ad7be681906498fadc422cf5efa2..eb17e920b3afb86731b4fb9914cee6aafd3ef487 100644
--- a/Source/core/xml/XMLSerializer.cpp
+++ b/Source/core/xml/XMLSerializer.cpp
@@ -1,6 +1,7 @@
 /*
  *  Copyright (C) 2003, 2006 Apple Inc. All rights reserved.
  *  Copyright (C) 2006 Samuel Weinig (sam@webkit.org)
+ *  Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
@@ -30,8 +31,10 @@ namespace WebCore {
 
 String XMLSerializer::serializeToString(Node* node, ExceptionState& es)
 {
-    if (!node)
+    if (!node) {
+        es.throwDOMException(TypeError, "Invalid node value.");
         return String();
+    }
 
     return createMarkup(node);
 }