Add missing null check to Context::GetCalling().

src/api.cc

 // Copyright 2009 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 2722 matching lines @@
 
 v8::Local<v8::Context> Context::GetCurrent() {
   if (IsDeadCheck("v8::Context::GetCurrent()")) return Local<Context>();
   i::Handle<i::Context> context(i::Top::global_context());
   return Utils::ToLocal(context);
 }
 
 
 v8::Local<v8::Context> Context::GetCalling() {
   if (IsDeadCheck("v8::Context::GetCalling()")) return Local<Context>();
-  i::Handle<i::Context> context(i::Top::GetCallingGlobalContext());
+  i::Handle<i::Object> calling = i::Top::GetCallingGlobalContext();
+  if (calling.is_null()) return Local<Context>();
+  i::Handle<i::Context> context = i::Handle<i::Context>::cast(calling);
   return Utils::ToLocal(context);
 }
 
 
 v8::Local<v8::Object> Context::Global() {
   if (IsDeadCheck("v8::Context::Global()")) return Local<v8::Object>();
   i::Object** ctx = reinterpret_cast<i::Object**>(this);
   i::Handle<i::Context> context =
       i::Handle<i::Context>::cast(i::Handle<i::Object>(ctx));
   i::Handle<i::Object> global(context->global_proxy());
@@ skipping 978 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* thread_local =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   thread_local->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal