code: public static <T extends Comparable<T>> RangeSet<T> unionRangeSets(final Iterable<RangeSet<T>> rangeSets)
    {
      final RangeSet<T> rangeSet = TreeRangeSet.create();
      for (RangeSet<T> set : rangeSets) {
        rangeSet.addAll(set);
      }
      return rangeSet;
    }
docs: Unions a set of rangeSets, or returns null if the set is empty.