Return error not null for date time format.

src/extensions/experimental/datetime-format.cc

Index: src/extensions/experimental/datetime-format.cc
===================================================================
--- src/extensions/experimental/datetime-format.cc	(revision 8679)
+++ src/extensions/experimental/datetime-format.cc	(working copy)
@@ -135,7 +135,7 @@
 v8::Handle<v8::Value> DateTimeFormat::GetWeekdays(const v8::Arguments& args) {
   icu::SimpleDateFormat* date_format = UnpackDateTimeFormat(args.Holder());
   if (!date_format) {
-    ThrowUnexpectedObjectError();
+    return ThrowUnexpectedObjectError();
   }
 
   const icu::DateFormatSymbols* symbols = date_format->getDateFormatSymbols();