code: public void traceOn(OutputStream traceStream) {
      if (traceStream == null) {
        throw new NullPointerException();
      } else {
        this.traceStream = new PrintWriter(new OutputStreamWriter(traceStream, StandardCharsets.UTF_8), true);
      }
    }
docs: Enables HTTP call tracing and written to traceStream.
  
  @param traceStream {@link OutputStream} for writing HTTP call tracing.
  
  @see #traceOff