public static <E extends @Nullable Object> SetView<E> union(
      final Set<? extends E> set1, final Set<? extends E> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public int size() {
        int size = set1.size();
        for (E e : set2) {
          if (!set1.contains(e)) {
            size++;
          }
        }
        return size;

				"application/x-appleworks",
				"application/x-archive",
				"application/x-arj",
				"application/x-authorware-bin",
				"application/x-authorware-map",
				"application/x-authorware-seg",
				"application/x-bcpio",
				"application/x-berkeley-db",
				"application/x-bibtex-text-file",
				"application/x-bittorrent",
				"application/x-bplist",
				"application/x-bzip",
				"application/x-bzip2",