* <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated. Instead,
   * use the {@code TreeSet} constructor directly, taking advantage of <a
   * href="http://goo.gl/iz2Wi">"diamond" syntax</a>. One caveat to this is that the {@code TreeSet}
   * constructor uses a null {@code Comparator} to mean "natural ordering," whereas this factory
   * rejects null. Clean your code accordingly.
   *