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());
  }

  public void testAsSet_absent() {