code: public void update(final ItemsSketch<T> sketchIn) {
      gadget_ = updateLogic(maxK_, comparator_, gadget_, sketchIn);
    }
docs: Iterative union operation, which means this method can be repeatedly called.
  Merges the given sketch into this union object.
  The given sketch is not modified.
  It is required that the ratio of the two K values be a power of 2.
  This is easily satisfied if each of the K values is already a power of 2.
  If the given sketch is null or empty it is ignored.
  
  <p>It is required that the results of the union operation, which can be obtained at any time,
  is obtained from {@link #getResult() }.</p>
  
  @param sketchIn the sketch to be merged into this one.