* avoid memory leaks when an element is no longer necessary.
   *
   * <p>This method accepts an array with element type {@code @Nullable T}, but callers must pass an
   * array whose contents are initially non-null. The {@code @Nullable} annotation indicates that
   * this method will write nulls into the array during iteration.
   *

      }
    }
    Arrays.fill(elements, uniques, n, null);
    if (uniques == 1) {
      // There is only one element or elements are all duplicates
      @SuppressWarnings("unchecked") // we are careful to only pass in E
      // requireNonNull is safe because the first `uniques` elements are non-null.
      E element = (E) requireNonNull(elements[0]);
      return new SingletonImmutableSet<E>(element);

  private enum SupplierFunctionImpl implements SupplierFunction<@Nullable Object> {
    INSTANCE;

    // Note: This makes T a "pass-through type"
    @Override
    @CheckForNull
    public Object apply(Supplier<@Nullable Object> input) {
      return input.get();
    }

    @Override
    public String toString() {

  // - @PolyNull means "@Nullable or @Nonnull"
  //   (That would be unsound for an input Iterable<@Nullable Foo>. So, if we wanted to use
  //   @PolyNull, we would have to restrict this method to non-null <T>. But it has users who pass
  //   iterables with null elements.)
  //
  // - @JointlyNullable means "@Nullable or no annotation"
  @CheckForNull
  public static <T extends @Nullable Object> T find(
      Iterable<? extends T> iterable,

   * take a principled stand on this, but the amount of such code is simply overwhelming. To avoid
   * creating a lot of compile errors that users would not find to be informative, we're giving in
   * and allowing callers to pass arguments that a nullness checker believes could be null.
   *
   * We still encourage people to use requireNonNull over checkNotNull for non-precondition checks.
   */

  /**

 * <td>{@link #base64()}
 * <td>A-Z a-z 0-9 + /
 * <td>1.33
 * <td>=
 * <td>
 * <tr>
 * <td>{@link #base64Url()}
 * <td>A-Z a-z 0-9 - _
 * <td>1.33
 * <td>=
 * <td>Safe to use as filenames, or to pass in URLs without escaping
 * </table>
 *
 * <p>All instances of this class are immutable, so they may be stored safely as static constants.
 *
 * @author Louis Wasserman
 * @since 14.0
 */

  }

  public void testGet_withDefault_negativePosition() {
    try {
      Iterables.get(newArrayList("a", "b", "c"), -1, "d");
      fail();
    } catch (IndexOutOfBoundsException expected) {
      // pass
    }
  }

  public void testGet_withDefault_simple() {
    ArrayList<String> list = newArrayList("a", "b", "c");
    assertEquals("b", Iterables.get(list, 1, "d"));
  }

 *
 * <p>The common ways to get an instance of {@code Ordering} are:
 *
 * <ul>
 *   <li>Subclass it and implement {@link #compare} instead of implementing {@link Comparator}
 *       directly
 *   <li>Pass a <i>pre-existing</i> {@link Comparator} instance to {@link #from(Comparator)}
 *   <li>Use the natural ordering, {@link Ordering#natural}
 * </ul>
 *
 * <h4>Chaining</h4>
 *

     * 1) An interface I extending Comparable<I> so that the created array is of
     * an interface type. 2) An instance of a class implementing that interface
     * so that we can pass non-null instances of the interface.
     *
     * (Currently it's safe to pass instances for which compareTo() always
     * returns 0, but if we had a SingletonImmutableSortedSet, this might no
     * longer be the case.)
     *

    list.add("a");
    list.add("b");
    Iterator<String> iterator = list.iterator();
    try {
      get(iterator, -1, "c");
      fail();
    } catch (IndexOutOfBoundsException expected) {
      // pass
    }
    assertTrue(iterator.hasNext());
  }

  public void testAdvance_basic() {
    List<String> list = newArrayList();
    list.add("a");
    list.add("b");