changeSink method
- StreamSink<T> change(- StreamSink<T> 
 
- StreamSink<
override
    Returns a copy of this with sink replaced by change's return
value.
Implementation
@override
StreamChannel<T> changeSink(StreamSink<T> Function(StreamSink<T>) change) =>
    StreamChannel.withCloseGuarantee(stream, change(sink));