code: public ProcessExecutor redirectError(OutputStream output) {
      if (output == null)
        output = NullOutputStream.NULL_OUTPUT_STREAM;
      PumpStreamHandler pumps = pumps();
      // Only set the error stream handler, preserve the same output stream handler
      streams(new PumpStreamHandler(pumps == null ? null : pumps.getOut(), output, pumps == null ? null : pumps.getInput()));
      redirectErrorStream(false);
      return this;
    }
docs: Redirects the process' error stream to given output stream.
  If this method is invoked multiple times each call overwrites the previous.
  Use {@link #redirectErrorAlsoTo(OutputStream)} if you want to redirect the error to multiple streams.
  <p>
  Calling this method automatically disables merging the process error stream to its output stream.
  </p>
  
  @param output output stream where the process error is redirected to (<code>null</code> means {@link NullOutputStream} which acts like a <code>/dev/null</code>).
  @return This process executor.