Add missing null-tests to async error functions.

sdk/lib/async/broadcast_stream_controller.dart

Index: sdk/lib/async/broadcast_stream_controller.dart
diff --git a/sdk/lib/async/broadcast_stream_controller.dart b/sdk/lib/async/broadcast_stream_controller.dart
index cda7c0f960c7ce16effca089b555da257c8c7bc8..3d09739bb56b14c0ef700a496cfef0ff073f5c2e 100644
--- a/sdk/lib/async/broadcast_stream_controller.dart
+++ b/sdk/lib/async/broadcast_stream_controller.dart
@@ -238,10 +238,12 @@ abstract class _BroadcastStreamController<T>
   }
 
   void addError(Object error, [StackTrace stackTrace]) {
+    if (error == null) throw new ArgumentError("Error must not be null");

[floitsch, 2014/09/24 12:59:14]

Or make it an asynchronous NullThrownError?

[Lasse Reichstein Nielsen, 2014/09/24 13:49:57]

I can do that everywhere. It would be consistent behavior, the only problem
would be that it wouldn't throw early if the value was null by error.

Let's do it.

     if (!_mayAddEvent) throw _addEventError();
     AsyncError replacement = Zone.current.errorCallback(error, stackTrace);

[Søren Gjesse, 2014/09/24 13:29:31]

The five lines seems to be duplicated in a number of places, refactor?

AsyncError replacement = Zone.current.errorCallback(error, stackTrace);
if (replacement != null) {
  error = replacement.error;
  if (error == null) error = new NullThrownError();
  stackTrace = replacement.stackTrace;
}

[Lasse Reichstein Nielsen, 2014/09/24 13:49:57]

I wish that I could, but it really just conditionally unpacks into local
variables, which is not something that can be abstracted away.
The only reusable option part would be a 'getAsyncError(AsyncError e) => e.error
== null ? new NullThrownError() : e.error;' to save one line each place. I'm not
sure it's worth it - but let's try and see.

I can't assume that the AsyncError is the current implementation, so it can't
prevent null errors, I have to check after extracting it.

     if (replacement != null) {
       error = replacement.error;
+      if (error == null) error = new NullThrownError();
       stackTrace = replacement.stackTrace;
     }
     _sendError(error, stackTrace);