code: public static <T> Set<T> union(final Collection<? extends T>... lists)
  	{
  		Set<T> s = new HashSet<T>();
  
  		for (Collection<? extends T> list : lists)
  			if (list != null)
  				s.addAll(list);
  
  		return s;
  	}
docs: Concatenates a number of Collections into a single Set
  
  @param <T>
  @param lists
  
  @return