Minor cleanup for the Null string case.

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
@@ skipping 3643 matching lines @@
   if (Api::StringGetPeerHelper(args, arg_index, peer)) {
     return Api::Success();
   }
   *peer = NULL;
   ReusableObjectHandleScope reused_obj_handle(isolate);
   Object& obj = reused_obj_handle.Handle();
   obj = arguments->NativeArgAt(arg_index);
   if (RawObject::IsStringClassId(obj.GetClassId())) {
     return Api::NewHandle(isolate, obj.raw());
   }
+  if (obj.IsNull()) {
+    return Api::Null();
+  }
   return Api::NewError("%s expects argument to be of"
                        " type String.", CURRENT_FUNC);
 }
 
 
 DART_EXPORT Dart_Handle Dart_GetNativeIntegerArgument(Dart_NativeArguments args,
                                                       int index,
                                                       int64_t* value) {
   TRACE_API_CALL(CURRENT_FUNC);
   NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);
@@ skipping 619 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart