```Python
say_hi()  # Oh, no, this throws an error! 😱
```

The `name` parameter is **still required** (not *optional*) because it doesn't have a default value. Still, `name` accepts `None` as the value:

```Python
say_hi(name=None)  # This works, None is valid 🎉
```

The good news is, in most cases, you will be able to simply use `|` to define unions of types:

```python
def say_hi(name: str | None):

And then you can return any object you need, as you normally would (a `dict`, a database model, etc).

And if you declared a `response_model`, it will still be used to filter and convert the object you returned.

**FastAPI** will use that *temporal* response to extract the headers (also cookies and status code), and will put them in the final response that contains the value you returned, filtered by any `response_model`.

   *       created by invoking the constructor or static factory method.
   *   <li>If there is any non-private constructor or non-private static factory method declared by
   *       {@code cls}:
   *       <ul>
   *         <li>Test will fail if default value for a parameter cannot be determined.

Cache Miss will be typical if the item has not been read from the network, is uncacheable, or is past it's
lifetime based on Response cache headers.

 - CallStart
 - **CacheMiss**
 - ProxySelectStart
 - ... Standard Events ...
 - CallEnd

### Conditional Cache Hit

When cache flags require checking the cache results are still valid an early cacheConditionalHit event is

   * [expectMoreExchanges].
   *
   * This will release the connection if it is still held.
   *
   * It will also notify the listener that the call completed; either successfully or
   * unsuccessfully.
   *
   * If the call was canceled or timed out, this will wrap [e] in an exception that provides that
   * additional context. Otherwise [e] is returned as-is.
   */

    /** Window size in bytes. */
    const val INITIAL_WINDOW_SIZE = 4

    /** HTTP/2: Size in bytes of the largest frame payload the sender will accept. */
    const val MAX_FRAME_SIZE = 5

    /** HTTP/2: Advisory only. Size in bytes of the largest header list the sender will accept. */
    const val MAX_HEADER_LIST_SIZE = 6

    /** Total number of settings. */
    const val COUNT = 10
  }

	// (https://code.google.com/p/android/issues/detail?id=3254), but it's
	// still broken on our builders in 2023. Instead, append the exitcode to
	// the output and parse it from there.
	filter, exitStr := newExitCodeFilter(os.Stdout)
	args += "; echo -n " + exitStr + "$?"

	cmd := adbCmd("exec-out", args)
	cmd.Stdout = filter
	// If the adb subprocess somehow hangs, go test will kill this wrapper

In the next sections you will see other options, configurations, and additional features.

/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first { #read-the-tutorial-first }

It had the best performance benchmarks at the time (only surpassed by Starlette).

At first, it didn't have an automatic API documentation web UI, but I knew I could add Swagger UI to it.

It had a dependency injection system. It required pre-registration of components, as other tools discussed above. But still, it was a great feature.

      Thread.currentThread().interrupt() // Retain interrupted status.
      throw InterruptedIOException()
    }
  }

  /**
   * The Okio timeout watchdog will call [timedOut] if the timeout is reached. In that case we close
   * the stream (asynchronously) which will notify the waiting thread.
   */
  internal inner class StreamTimeout : AsyncTimeout() {
    override fun timedOut() {
      closeLater(ErrorCode.CANCEL)