/**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.

        throw PermittedMetaException.ISE;
      }
    }

    private List<E> getElements() {
      List<E> elements = new ArrayList<>();
      Helpers.addAll(elements, previousElements);
      Helpers.addAll(elements, Helpers.reverse(nextElements));
      return elements;
    }
  }

  public enum KnownOrder {
    KNOWN_ORDER,
    UNKNOWN_ORDER
  }

     * any of the algorithm name is not supported. The returned collection has equal count of elements as passed in
     * collection of names, and if names contains duplicated elements, the returned list of algorithms will have
     * duplicates as well.
     *
     * @throws ChecksumAlgorithmServiceException if any asked algorithm name is not supported.

    return new Strings();
  }

  @Override
  public Set<String> create(Object... elements) {
    String[] array = new String[elements.length];
    int i = 0;
    for (Object e : elements) {
      array[i++] = (String) e;
    }
    return create(array);
  }

  protected abstract Set<String> create(String[] elements);

  @Override
  public String[] createArray(int length) {
    return new String[length];
  }

  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
  public void testEquals_containingNull() {
    ArrayList<E> elements = new ArrayList<>(getSampleElements());
    elements.set(elements.size() / 2, null);
    collection = getSubjectGenerator().create(elements.toArray());
    List<E> other = new ArrayList<>(getSampleElements());
    assertFalse(

  public SampleElements<Entry<K, V>> samples() {
    return SampleElements.mapEntries(keys, values);
  }

  @Override
  public Set<Entry<K, V>> create(Object... elements) {
    Entry<K, V>[] entries = createArray(elements.length);
    arraycopy(elements, 0, entries, 0, elements.length);
    return createFromEntries(entries);
  }

  public abstract Set<Entry<K, V>> createFromEntries(Entry<K, V>[] entries);

  @Override

        return elements;
    }

    /**
     * Returns an array of {@literal byte}.
     *
     * @param elements the elements of the array
     * @return the array
     */
    public static byte[] asByteArray(final byte... elements) {
        return elements;
    }

    /**
     * Returns an array of {@literal short}.
     *
     * @param elements the elements of the array
     * @return the array

   * Creates a {@code CompactLinkedHashSet} instance containing the given elements in unspecified
   * order.
   *
   * @param elements the elements that the set should contain
   * @return a new {@code CompactLinkedHashSet} containing those elements (minus duplicates)
   */
  @SafeVarargs
  public static <E extends @Nullable Object> CompactLinkedHashSet<E> create(E... elements) {
    CompactLinkedHashSet<E> set = createWithExpectedSize(elements.length);

              public Collection<String> create(String[] elements) {
                // TODO: MinimalCollection should perhaps throw
                for (Object element : elements) {
                  if (element == null) {
                    throw new NullPointerException();
                  }
                }
                return MinimalCollection.of(elements);
              }
            })

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    return CompactHashSet.create(asList(elements));
                  }
                })
            .named("CompactHashSet")
            .withFeatures(allFeatures)
            .createTestSuite());
    suite.addTest(