Add missing null-tests to async error functions.

sdk/lib/async/broadcast_stream_controller.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 class _BroadcastStream<T> extends _ControllerStream<T> {
   _BroadcastStream(_StreamControllerLifecycle controller) : super(controller);
 
   bool get isBroadcast => true;
@@ skipping 220 matching lines @@
     assert(_isAddingStream);
     return new StateError("Cannot add new events while doing an addStream");
   }
 
   void add(T data) {
     if (!_mayAddEvent) throw _addEventError();
     _sendData(data);
   }
 
   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);
   }
 
   Future close() {
     if (isClosed) {
       assert(_doneFuture != null);
       return _doneFuture;
     }
@@ skipping 247 matching lines @@
     _pauseCount++;
   }
   void resume() { _resume(null); }
   void _resume(_) {
     if (_pauseCount > 0) _pauseCount--;
   }
   Future cancel() { return new _Future.immediate(null); }
   bool get isPaused => _pauseCount > 0;
   Future asFuture([Object value]) => new _Future();
 }