* <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
   * of values that will be added, if that knowledge is readily available. It is better to guess a
   * value slightly too high than slightly too low. If the value is not exact, the {@link
   * ImmutableDoubleArray} that is built will very likely occupy more memory than strictly
   * necessary; to trim memory usage, build using {@code builder.build().trimmed()}.

        if (firstTimeSeeingThisException) {
          log(throwable);
          return;
        }
      }
    }

    /*
     * TODO(cpovirk): Should whenAllComplete().call*() log errors, too? Currently, it doesn't call
     * handleException() at all.
     */
    if (throwable instanceof Error) {
      /*
       * TODO(cpovirk): Do we really want to log this if we called setException(throwable) and it

                + expected
                + ", actual = "
                + actual);
      }
    }

    if (expectedIter.hasNext() || actualIter.hasNext()) {
      // actual either had too few or too many elements
      fail(
          "contents were not equal and in the same order: "
              + "expected = "
              + expected
              + ", actual = "
              + actual);
    }

    /*
     * This test will catch problems where the underlying iterator
     * throws a RuntimeException when retrieving the nth element.
     *
     * If the PeekingIterator is caching elements too aggressively,
     * it may throw the exception on the (n-1)th element (oops!).
     */

    /* Checks the case where the first element throws an exception. */

    List<Integer> list = emptyList();

  }

  public void testAsMultimap() {
    ImmutableMap<String, Integer> map =
        ImmutableMap.of("one", 1, "won", 1, "two", 2, "too", 2, "three", 3);
    ImmutableSetMultimap<String, Integer> expected =
        ImmutableSetMultimap.of("one", 1, "won", 1, "two", 2, "too", 2, "three", 3);
    assertEquals(expected, map.asMultimap());
  }

  public void testAsMultimapWhenEmpty() {

<img src="/img/tutorial/path-operation-advanced-configuration/image01.png">

And if you see the resulting OpenAPI (at `/openapi.json` in your API), you will see your extension as part of the specific *path operation* too:

```JSON hl_lines="22"
{
    "openapi": "3.1.0",
    "info": {
        "title": "FastAPI",
        "version": "0.1.0"
    },
    "paths": {
        "/items/": {
            "get": {

    /*
     * This test will catch problems where the underlying iterator
     * throws a RuntimeException when retrieving the nth element.
     *
     * If the PeekingIterator is caching elements too aggressively,
     * it may throw the exception on the (n-1)th element (oops!).
     */

    /* Checks the case where the first element throws an exception. */

    List<Integer> list = emptyList();

We already know that this method is related to the **items** because that word is in the `ItemsService` (taken from the tag), but we still have the tag name prefixed in the method name too. 😕

We will probably still want to keep it for OpenAPI in general, as that will ensure that the operation IDs are **unique**.

    if (in.read() == -1) {
      // oh, there's the end of the stream
      return combineBuffers(bufs, MAX_ARRAY_LEN);
    } else {
      throw new OutOfMemoryError("input is too large to fit in a byte array");
    }
  }

  private static byte[] combineBuffers(Queue<byte[]> bufs, int totalLen) {
    if (bufs.isEmpty()) {
      return new byte[0];
    }

### Generic types with type parameters

There are some data structures that can contain other values, like `dict`, `list`, `set` and `tuple`. And the internal values can have their own type too.

These types that have internal types are called "**generic**" types. And it's possible to declare them, even with their internal types.