static OutputStream teeOutputStream(final OutputStream a, final OutputStream b) {
  if (a == null) ret b;
  if (b == null) ret a;
  ret new OutputStream {
    public void write(int byt) throws IOException {
      a.write(byt);
      b.write(byt);
    }
    
    public void write(byte[] byt, int off, int len) throws IOException {
      a.write(byt, off, len);
      b.write(byt, off, len);
    }
  };
}

Began life as a copy of #1017323