code: public void update(final ArrayOfDoublesSketch sketchIn) {
      if (sketchIn == null) { return; }
      Util.checkSeedHashes(seedHash_, sketchIn.getSeedHash());
      if (sketch_.getNumValues() != sketchIn.getNumValues()) {
        throw new SketchesArgumentException("Incompatible sketches: number of values mismatch "
            + sketch_.getNumValues() + " and " + sketchIn.getNumValues());
      }
      if (sketchIn.isEmpty()) { return; }
      if (sketchIn.getThetaLong() < theta_) { theta_ = sketchIn.getThetaLong(); }
      final ArrayOfDoublesSketchIterator it = sketchIn.iterator();
      while (it.next()) {
        sketch_.merge(it.getKey(), it.getValues());
      }
    }
docs: Updates the union by adding a set of entries from a given sketch
  @param sketchIn sketch to add to the union