code: public Writer openBufferedStream() throws IOException {
      Writer writer = openStream();
      return (writer instanceof BufferedWriter)
          ? (BufferedWriter) writer
          : new BufferedWriter(writer);
    }
docs: Opens a new buffered {@link Writer} for writing to this sink. The returned stream is not
  required to be a {@link BufferedWriter} in order to allow implementations to simply delegate to
  {@link #openStream()} when the stream returned by that method does not benefit from additional
  buffering. This method returns a new, independent writer each time it is called.
  
  <p>The caller is responsible for ensuring that the returned writer is closed.
  
  @throws IOException if an I/O error occurs while opening the writer
  @since 15.0 (in 14.0 with return type {@link BufferedWriter})