code: public void update(final Sketch<S> sketchIn) {
      if (sketchIn == null || sketchIn.isEmpty()) { return; }
      if (sketchIn.theta_ < theta_) { theta_ = sketchIn.theta_; }
      final SketchIterator<S> it = sketchIn.iterator();
      while (it.next()) {
        sketch_.merge(it.getKey(), it.getSummary(), summarySetOps_);
      }
    }
docs: Updates the internal set by adding entries from the given sketch
  @param sketchIn input sketch to add to the internal set