docs: public void update(final ArrayOfDoublesSketch sketchIn, final ArrayOfDoublesCombiner combiner) {
      final boolean isFirstCall = isFirstCall_;
      isFirstCall_ = false;
      if (sketchIn == null) {
        isEmpty_ = true;
        sketch_ = null;
        return;
      }
      Util.checkSeedHashes(seedHash_, sketchIn.getSeedHash());
      theta_ = min(theta_, sketchIn.getThetaLong());
      isEmpty_ |= sketchIn.isEmpty();
      if (isEmpty_ || sketchIn.getRetainedEntries() == 0) {
        sketch_ = null;
        return;
      }
      if (isFirstCall) {
        sketch_ = createSketch(sketchIn.getRetainedEntries(), numValues_, seed_);
        final ArrayOfDoublesSketchIterator it = sketchIn.iterator();
        while (it.next()) {
          sketch_.insert(it.getKey(), it.getValues());
        }
      } else { //not the first call
        final int matchSize = min(sketch_.getRetainedEntries(), sketchIn.getRetainedEntries());
        final long[] matchKeys = new long[matchSize];
        final double[][] matchValues = new double[matchSize][];
        int matchCount = 0;
        final ArrayOfDoublesSketchIterator it = sketchIn.iterator();
        while (it.next()) {
          final double[] values = sketch_.find(it.getKey());
          if (values != null) {
            matchKeys[matchCount] = it.getKey();
            matchValues[matchCount] = combiner.combine(values, it.getValues());
            matchCount++;
          }
        }
        sketch_ = null;
        if (matchCount > 0) {
          sketch_ = createSketch(matchCount, numValues_, seed_);
          for (int i = 0; i < matchCount; i++) {
            sketch_.insert(matchKeys[i], matchValues[i]);
          }
        }
        if (sketch_ != null) {
          sketch_.setThetaLong(theta_);
          sketch_.setNotEmpty();
        }
      }
    }