// When a listener is first added, we run a task that will wait for the delegate to finish,
      // and when it is done will run the listeners.
      if (hasListeners.compareAndSet(false, true)) {
        if (delegate.isDone()) {
          // If the delegate is already done, run the execution list immediately on the current
          // thread.
          executionList.execute();
          return;
        }

`Optional[Something]` é na verdade um atalho para `Union[Something, None]`, eles são equivalentes.

Isso também significa que no Python 3.10, você pode utilizar `Something | None`:

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```

          <version>4.0.0+</version>
          <required>false</required>
          <description>Default dependency information for projects that inherit from this one. The
            dependencies in this section are not immediately resolved. Instead, when a POM derived
            from this one declares a dependency described by a matching groupId and artifactId, the

    "bar": {"id": "bar", "title": "Bar", "description": "The bartenders"},
}

app = FastAPI()


class Item(BaseModel):
    id: str
    title: str
    description: Union[str, None] = None


@app.get("/items/{item_id}", response_model=Item)
async def read_main(item_id: str, x_token: str = Header()):
    if x_token != fake_secret_token:

			go func(i int, set *erasureObjects) {
				defer wg.Done()
				err := set.listPath(listCtx, o, innerResults)
				mu.Lock()
				defer mu.Unlock()
				if err == nil {
					allAtEOF = false
				}
				errs[i] = err
			}(len(errs), set)
			errs = append(errs, nil)
		}
	}
	mu.Unlock()

	// Gather results to a single channel.
	// Quorum is one since we are merging across sets.

    return doBackward(uncheckedCastNullableTToT(b));
  }

  /**
   * Returns an iterable that applies {@code convert} to each element of {@code fromIterable}. The
   * conversion is done lazily.
   *
   * <p>The returned iterable's iterator supports {@code remove()} if the input iterator does. After
   * a successful {@code remove()} call, {@code fromIterable} no longer contains the corresponding
   * element.

  private fun acceptConnections() {
    while (true) {
      val socket: Socket
      try {
        socket = serverSocket!!.accept()
      } catch (e: SocketException) {
        logger.fine("${this@MockWebServer} done accepting connections: ${e.message}")
        return
      }

      val socketPolicy = dispatcher.peek().socketPolicy
      if (socketPolicy === DisconnectAtStart) {
        dispatchBookkeepingRequest(0, socket)

    immutable = immutable,
    headerValue = headerValue,
  )
}

/**
 * Returns the next index in this at or after [startIndex] that is a character from
 * [characters]. Returns the input length if none of the requested characters can be found.
 */
private fun String.indexOfElement(
  characters: String,
  startIndex: Int = 0,
): Int {
  for (i in startIndex until length) {
    if (this[i] in characters) {

      taskRunner = taskRunner,
      maxIdleConnections = maxIdleConnections,
      keepAliveDuration = 100L,
      timeUnit = TimeUnit.NANOSECONDS,
      connectionListener = ConnectionListener.NONE,
      exchangeFinderFactory = { pool, address, user ->
        FastFallbackExchangeFinder(
          routePlanner ?: RealRoutePlanner(
            taskRunner = taskRunner,
            connectionPool = pool,

    route: Route?,
    response: Response,
  ): Request?

  companion object {
    /** An authenticator that knows no credentials and makes no attempt to authenticate. */
    @JvmField
    val NONE: Authenticator = AuthenticatorNone()

    private class AuthenticatorNone : Authenticator {
      override fun authenticate(
        route: Route?,
        response: Response,
      ): Request? = null
    }