}

  public void testToOptionalSingleton() {
    assertThat(Stream.of(1).collect(toOptional())).hasValue(1);
  }

  public void testToOptionalNull() {
    Stream<@Nullable Object> stream = Stream.of((Object) null);
    assertThrows(NullPointerException.class, () -> stream.collect(toOptional()));
  }

  public void testToOptionalMultiple() {
    IllegalArgumentException expected =

 *
 * @param <B> the common supertype that all values will share. When in doubt, just use {@link
 *     Object}, or use {@code @Nullable Object} to allow null values.
 * @since 2.0
 */
@DoNotMock("Use ImmutableClassToInstanceMap or MutableClassToInstanceMap")
@GwtCompatible
public interface ClassToInstanceMap<B extends @Nullable Object>
    extends Map<Class<? extends @NonNull B>, B> {
  /**

                    "type": "object",
                    "properties": {
                        "item": {"$ref": "#/components/schemas/Item"},
                        "item2": {"$ref": "#/components/schemas/Item"},
                    },
                },
                "HTTPValidationError": {
                    "title": "HTTPValidationError",
                    "type": "object",
                    "properties": {

                    "type": "object",
                    "properties": {
                        "x": {"title": "X", "type": "number"},
                        "y": {"title": "Y", "type": "number"},
                    },
                },
                "HTTPValidationError": {
                    "title": "HTTPValidationError",
                    "type": "object",
                    "properties": {

                    "title": "Offer",
                    "type": "object",
                },
                "ValidationError": {
                    "title": "ValidationError",
                    "required": ["loc", "msg", "type"],
                    "type": "object",
                    "properties": {
                        "loc": {
                            "title": "Location",

  // Comparison and hashing

  /**
   * Compares the specified object with this multiset for equality. Returns {@code true} if the
   * given object is also a multiset and contains equal elements with equal counts, regardless of
   * order.
   */
  @Override
  // TODO(kevinb): caveats about equivalence-relation?
  boolean equals(@Nullable Object object);

  /**

  private static final RangeMap<Comparable<?>, Object> EMPTY_SUB_RANGE_MAP =
      new RangeMap<Comparable<?>, Object>() {
        @Override
        public @Nullable Object get(Comparable<?> key) {
          return null;
        }

        @Override
        public @Nullable Entry<Range<Comparable<?>>, Object> getEntry(Comparable<?> key) {
          return null;
        }

  public final Set<Feature<?>> getAbsentFeatures() {
    return absentFeatures;
  }

  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof TesterRequirements) {
      TesterRequirements that = (TesterRequirements) object;
      return this.presentFeatures.equals(that.presentFeatures)
          && this.absentFeatures.equals(that.absentFeatures);
    }

    /**
     * Method setFileComment.
     *
     * @param fileComment a fileComment object.
     */
    public void setFileComment(String fileComment) {
        delegate.setFileComment(fileComment);
    }

    /**
     * Method write.
     *
     * @param writer   a writer object
     * @param metadata a Metadata object
     * @throws java.io.IOException java.io.IOException if any
     */

    this.delegate = delegate;
    this.delegateList = delegateList;
  }

  RegularImmutableAsList(ImmutableCollection<E> delegate, Object[] array) {
    this(delegate, asImmutableList(array));
  }

  RegularImmutableAsList(ImmutableCollection<E> delegate, Object[] array, int size) {
    this(delegate, asImmutableList(array, size));
  }

  @Override
  ImmutableCollection<E> delegateCollection() {