assertThat(Stream.empty().collect(toOptional())).isEmpty();
  }

  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() {

   * @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.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

   * iterable is empty.
   *
   * <p><b>Java 8+ users:</b> the {@code Stream} equivalent to this method is {@code
   * stream.collect(MoreCollectors.toOptional()).orElse(defaultValue)}.
   *
   * @throws IllegalArgumentException if the iterator contains multiple elements
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(

   * iterable is empty.
   *
   * <p><b>Java 8+ users:</b> the {@code Stream} equivalent to this method is {@code
   * stream.collect(MoreCollectors.toOptional()).orElse(defaultValue)}.
   *
   * @throws IllegalArgumentException if the iterator contains multiple elements
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(

 * @since 10.0
 */
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {
    return Absent.withType();
  }

    exclusiveMaximum: Optional[float] = None
    minimum: Optional[float] = None
    exclusiveMinimum: Optional[float] = None
    maxLength: Optional[int] = Field(default=None, ge=0)
    minLength: Optional[int] = Field(default=None, ge=0)
    pattern: Optional[str] = None
    maxItems: Optional[int] = Field(default=None, ge=0)
    minItems: Optional[int] = Field(default=None, ge=0)
    uniqueItems: Optional[bool] = None

    p: Optional[str] = None


@app.get("/model-optional-str")
async def read_model_optional_str(p: Annotated[CookieModelOptionalStr, Cookie()]):
    return {"p": p.p}


@pytest.mark.parametrize(
    "path",
    ["/optional-str", "/model-optional-str"],
)
def test_optional_str_schema(path: str):
    assert app.openapi()["paths"][path]["get"]["parameters"] == [
        {
            "required": False,

class HeaderModelOptionalListStr(BaseModel):
    p: Optional[list[str]] = None


@app.get("/model-optional-list-str")
async def read_model_optional_list_str(
    p: Annotated[HeaderModelOptionalListStr, Header()],
):
    return {"p": p.p}


@pytest.mark.parametrize(
    "path",
    ["/optional-list-str", "/model-optional-list-str"],
)
def test_optional_list_str_schema(path: str):

            return Optional.of(Boolean.TRUE);
        }
        return Optional.empty();
    }

    @Override
    public Optional<Boolean> updateSnapshots() {
        if (commandLine.hasOption(CLIManager.UPDATE_SNAPSHOTS)) {
            return Optional.of(Boolean.TRUE);
        }
        return Optional.empty();
    }

    @Override
    public Optional<List<String>> activatedProfiles() {

):
    return {"p": p}


class FormModelOptionalListStr(BaseModel):
    p: Optional[list[str]] = None


@app.post("/model-optional-list-str", operation_id="model_optional_list_str")
async def read_model_optional_list_str(p: Annotated[FormModelOptionalListStr, Form()]):
    return {"p": p.p}


@pytest.mark.parametrize(
    "path",