Return error not null for date time format.

src/extensions/experimental/datetime-format.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 117 matching lines @@
       icu::DateFormatSymbols::STANDALONE,
       icu::DateFormatSymbols::WIDE);
 
   return GetSymbols(
       args, narrow, narrow_count, abbrev, abbrev_count, wide, wide_count);
 }
 
 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();
 
   int32_t narrow_count;
   const icu::UnicodeString* narrow = symbols->getWeekdays(
       narrow_count,
       icu::DateFormatSymbols::STANDALONE,
       icu::DateFormatSymbols::NARROW);
   int32_t abbrev_count;
@@ skipping 226 matching lines @@
   } else if (type == UNICODE_STRING_SIMPLE("long")) {
     return icu::DateFormat::kLong;
   } else if (type == UNICODE_STRING_SIMPLE("full")) {
     return icu::DateFormat::kFull;
   }
 
   return icu::DateFormat::kShort;
 }
 
 } }  // namespace v8::internal