code: public void unionWith(Multiset<O> multiset) throws ParameterException {
  		Validate.notNull(multiset);
  		for (O o : multiset.support()) {
  			setMultiplicity(o, Math.max(multiplicity(o), multiset.multiplicity(o)));
  		}
  	}
docs: Combines this multiset with the given multiset.<br>
  This operation changes only this multiset, not the given one.
  
  @param multiset The multiset to include.
  @throws ParameterException