return new Present<>(
        checkNotNull(
            function.apply(reference),
            "the Function passed to Optional.transform() must not return null."));
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    if (obj instanceof Present) {
      Present<?> other = (Present<?>) obj;
      return reference.equals(other.reference);
    }

     *         element.
     */
    @Override
    public boolean add(final E o) {
        return map.put(o, PRESENT) == null;
    }

    /**
     * Removes the specified element from this set if it is present.
     *
     * @param o
     *            object to be removed from this set, if present.
     * @return true if the set contained the specified element.
     */
    @Override

            : Lists.<@Nullable Present<V>>newArrayListWithCapacity(futures.size());

    // Populate the results list with null initially.
    for (int i = 0; i < futures.size(); ++i) {
      values.add(null);
    }

    this.values = values;
  }

  @Override
  final void collectOneValue(int index, @ParametricNullness V returnValue) {
    @RetainedLocalRef List<@Nullable Present<V>> localValues = values;

        // Verify the field naming is set to CAMEL_TO_LOWER_SNAKE
        OptionalThing<JsonFieldNaming> fieldNamingOpt = option.getFieldNaming();
        assertTrue("Field naming should be present", fieldNamingOpt.isPresent());
        assertEquals(JsonFieldNaming.CAMEL_TO_LOWER_SNAKE, fieldNamingOpt.get());
    }

    public void test_provideMappingOption_notNull() {
        // Test that mapping option is never null

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRemove_occurrences_present() {
    assertEquals(
        "multiset.remove(present, 2) didn't return the old count",
        1,
        getMultiset().remove(e0(), 2));
    assertFalse(
        "multiset contains present after multiset.remove(present, 2)",
        getMultiset().contains(e0()));
    assertEquals(0, getMultiset().count(e0()));
  }

  @CollectionSize.Require(SEVERAL)

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRemove_occurrences_present() {
    assertEquals(
        "multiset.remove(present, 2) didn't return the old count",
        1,
        getMultiset().remove(e0(), 2));
    assertFalse(
        "multiset contains present after multiset.remove(present, 2)",
        getMultiset().contains(e0()));
    assertEquals(0, getMultiset().count(e0()));
  }

  @CollectionSize.Require(SEVERAL)

        assertNotNull("Retention annotation should be present", retention);
        assertEquals("Retention should be RUNTIME", RetentionPolicy.RUNTIME, retention.value());
    }

    // Test annotation target elements
    public void test_targetElements() {
        final Target target = CustomSize.class.getAnnotation(Target.class);
        assertNotNull("Target annotation should be present", target);

        assertNotNull("Retention annotation should be present", retention);
        assertEquals("Retention should be RUNTIME", RetentionPolicy.RUNTIME, retention.value());
    }

    // Test annotation target elements
    public void test_targetElements() {
        final Target target = UriType.class.getAnnotation(Target.class);
        assertNotNull("Target annotation should be present", target);

  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPut_unsupportedPresentExistingValue() {
    try {
      assertEquals("put(present, existingValue) should return present or throw", v0(), put(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)

  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPut_unsupportedPresentExistingValue() {
    try {
      assertEquals("put(present, existingValue) should return present or throw", v0(), put(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)