doOnError method
Invokes the given callback function when the stream emits an error.
Example
Stream.error(Exception())
  .doOnError((error, stacktrace) => print('oh no'))
  .listen(null); // prints 'Oh no'
Implementation
Stream<T> doOnError(void Function(Object, StackTrace) onError) =>
    DoStreamTransformer<T>(onError: onError).bind(this);