docs: public void update(final ReservoirItemsSketch<T> sketchIn) {
      if (sketchIn == null) {
        return;
      }
  
      final ReservoirItemsSketch<T> ris =
          (sketchIn.getK() <= maxK_ ? sketchIn : sketchIn.downsampledCopy(maxK_));
  
      // can modify the sketch if we downsampled, otherwise may need to copy it
      final boolean isModifiable = (sketchIn != ris);
      if (gadget_ == null) {
        createNewGadget(ris, isModifiable);
      } else {
        twoWayMergeInternal(ris, isModifiable);
      }
    }