@Nonnull
    public static <T> Traverser<T> traverseSpliterator(@Nonnull Spliterator<T> spliterator) {
        return new SpliteratorTraverser<>(spliterator);
    }
@Test(expected = NullPointerException.class)
    public void when_traverseSpliteratorWithNull_then_failure() {
        Traverser<Integer> trav = traverseSpliterator(Stream.of(1, null).spliterator());
        trav.next();
        trav.next();
    }