public void testAddAll_nullCollectionReference() {
    assertThrows(NullPointerException.class, () -> collection.addAll(null));
  }

  /**
   * Returns the {@link Method} instance for {@link #testAddAll_nullUnsupported()} so that tests can
   * suppress it with {@code FeatureSpecificTestSuiteBuilder.suppressing()} until <a
   * href="https://bugs.openjdk.org/browse/JDK-5045147">JDK-5045147</a> is fixed.
   */
  @J2ktIncompatible

But a variable like `user-agent` is invalid in Python.

So, by default, `Header` will convert the parameter names characters from underscore (`_`) to hyphen (`-`) to extract and document the headers.

Also, HTTP headers are case-insensitive, so, you can declare them with standard Python style (also known as "snake_case").

    // NOTE: If we ever want to use a custom executor here, have a look at CombinedFuture as we'll
    // need to handle RejectedExecutionException

    if (allMustSucceed) {
      // We need fail fast, so we have to keep track of which future failed so we can propagate
      // the exception immediately

      // Register a listener on each Future in the list to update the state of this future.

Up to now, you have been declaring the parts of the request that you need with their types.

Taking data from:

* The path as parameters.
* Headers.
* Cookies.
* etc.

And by doing so, **FastAPI** is validating that data, converting it and generating documentation for your API automatically.

But there are situations where you might need to access the `Request` object directly.

Each section gradually builds on the previous ones, but it's structured to separate topics, so that you can go directly to any specific one to solve your specific API needs.

It is also built to work as a future reference so you can come back and see exactly what you need.

## Run the code { #run-the-code }

   * range [0, k) and ignore the remaining elements.
   */
  private final @Nullable T[] buffer;
  private int bufferSize;

  /**
   * The largest of the lowest k elements we've seen so far relative to this comparator. If
   * bufferSize ≥ k, then we can ignore any elements greater than this value.
   */
  private @Nullable T threshold;

So we have a dedicated thread for every socket that just reads frames and dispatches them.

  }

  private static <N, E> Map<N, NetworkConnections<N, E>> getNodeConnections(Network<N, E> network) {
    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
    // whatever ordering the network's nodes do, so ImmutableSortedMap is unnecessary even if the
    // input nodes are sorted.
    ImmutableMap.Builder<N, NetworkConnections<N, E>> nodeConnections = ImmutableMap.builder();

So, what we will do next is add the code to document how that *external API* should look like to receive the callback from *your API*.

{* ../../docs_src/path_params/tutorial001_py310.py hl[6:7] *}

The value of the path parameter `item_id` will be passed to your function as the argument `item_id`.

So, if you run this example and go to [http://127.0.0.1:8000/items/foo](http://127.0.0.1:8000/items/foo), you will see a response of:

```JSON
{"item_id":"foo"}
```