NullStreamSink<T> class Null safety

A StreamSink that discards all events.

The sink silently drops events until close is called, at which point it throws StateErrors when events are added. This is the same behavior as a sink whose remote end has closed, such as when a WebSocket connection has been closed.

This can be used when a sink is needed but no events are actually intended to be added. The NullStreamSink.error constructor can be used to represent errors when creating a sink, since StreamSink.done exposes sink errors. For example:

StreamSink<List<int>> openForWrite(String filename) {
  try {
    return RandomAccessSink(File(filename).openSync());
  } on IOException catch (error, stackTrace) {
    return NullStreamSink.error(error, stackTrace);
  }
}