assertEquals("correct", f.apply(new Object()));
    assertEquals("correct", f.apply(null));

    Function<@Nullable Object, @Nullable String> g = Functions.constant(null);
    assertEquals(null, g.apply(2));
    assertEquals(null, g.apply(null));

    new EqualsTester()
        .addEqualityGroup(f, Functions.constant("correct"))

 * <pre>{@code
 * // Find child element
 * Element child = parent.child("version").orElse(null);
 *
 * // Check if child exists
 * boolean hasVersion = parent.child("version").isPresent();
 *
 * // Get child text content
 * String version = parent.child("version")
 *     .map(Element::textContent)
 *     .orElse(null);
 *
 * // Get trimmed text content
 * String trimmedVersion = parent.child("version")

   *
   * @param escaper the non-null escaper to test
   */
  public static void assertBasic(Escaper escaper) throws IOException {
    // Escapers operate on characters: no characters, no escaping.
    Assert.assertEquals("", escaper.escape(""));
    // Assert that escapers throw null pointer exceptions.
    try {
      escaper.escape((String) null);

interface ModelCacheTag<T> {

    /**
     * Gets the name of the tag.
     *
     * @return The name of the tag, must not be {@code null}.
     */
    String getName();

    /**
     * Gets the type of data associated with this tag.
     *
     * @return The type of data, must not be {@code null}.
     */
    Class<T> getType();

    /**

   *
   * @param escaper the non-null escaper to test
   */
  public static void assertBasic(Escaper escaper) throws IOException {
    // Escapers operate on characters: no characters, no escaping.
    Assert.assertEquals("", escaper.escape(""));
    // Assert that escapers throw null pointer exceptions.
    try {
      escaper.escape((String) null);

  public void testPutIfAbsent_nullKeyUnsupported() {
    assertThrows(NullPointerException.class, () -> getMap().putIfAbsent(null, v3()));
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)

    private Map<TransferResource, Long> downloads = new ConcurrentHashMap<>();

    private int lastLength;

    public ConsoleTransferListener() {
        this(null);
    }

    public ConsoleTransferListener(PrintStream out) {
        this.out = (out != null) ? out : System.out;
    }

    @Override
    public void transferInitiated(TransferEvent event) {

  public void testContainsEntryNullYes() {
    initMultimapWithNullKeyAndValue();
    assertTrue(multimap().containsEntry(null, null));
  }

  @MapFeature.Require({ALLOWS_NULL_KEY_QUERIES, ALLOWS_NULL_VALUE_QUERIES})
  public void testContainsEntryNullNo() {
    assertFalse(multimap().containsEntry(null, null));
  }

  @MapFeature.Require(absent = ALLOWS_NULL_KEY_QUERIES)

     *
     * @param model The model whose duplicate elements should be merged, must not be {@code null}.
     * @param request The model building request that holds further settings, must not be {@code null}.
     * @param problems The container used to collect problems that were encountered, must not be {@code null}.
     */
    void mergeDuplicates(Model model, ModelBuildingRequest request, ModelProblemCollector problems);

    /**

    Cell[] as;
    long b, v;
    int[] hc;
    Cell a;
    int n;
    if ((as = cells) != null || !casBase(b = base, b + x)) {
      boolean uncontended = true;
      if ((hc = threadHashCode.get()) == null
          || as == null
          || (n = as.length) < 1
          || (a = as[(n - 1) & hc[0]]) == null
          || !(uncontended = a.cas(v = a.value, v + x))) retryUpdate(x, hc, uncontended);
    }
  }