code: @GwtCompatible(serializable = true)
    @SuppressWarnings("unchecked") // TODO(kevinb): right way to explain this??
    public static <C extends Comparable> Ordering<C> natural() {
      return (Ordering<C>) NaturalOrdering.INSTANCE;
    }
docs: Returns a serializable ordering that uses the natural order of the values. The ordering throws
  a {@link NullPointerException} when passed a null parameter.
  
  <p>The type specification is {@code <C extends Comparable>}, instead of the technically correct
  {@code <C extends Comparable<? super C>>}, to support legacy types from before Java 5.
  
  <p><b>Java 8 users:</b> use {@link Comparator#naturalOrder} instead.