}

  @SuppressWarnings("OptionalOfRedundantMethod") // Unit tests for Optional
  public void testOrNull_present() {
    assertEquals("a", Optional.of("a").orNull());
  }

  public void testOrNull_absent() {
    assertThat(Optional.absent().orNull()).isNull();
  }

  public void testAsSet_present() {
    Set<String> expected = Collections.singleton("a");
    assertEquals(expected, Optional.of("a").asSet());

      new Function<Optional<?>, @Nullable Object>() {
        @Override
        public @Nullable Object apply(Optional<?> optional) {
          return optional.orNull();
        }
      };

  /**
   * Sets.cartesianProduct doesn't allow sets that contain null, but we want null to mean "don't