- [ ] Ensure that tests pass locally: `./gradlew <changed-subproject>:quickTest`.

### Reviewing cheatsheet

Before merging the PR, comments starting with 
- ❌ ❓**must** be fixed
- 🤔 💅 **should** be fixed
- 💭 **may** be fixed

        // Assert: first page
        assertTrue(it.hasNext(), "Iterator should have first element");
        assertSame(fe1, it.next(), "First element must match first page");
        assertTrue(it.hasNext(), "Iterator should have second element");
        assertSame(fe2, it.next(), "Second element must match first page");

        // Next page fetched via fetchMore()

    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");
    checkNotNull(executor, "Executor was null.");

    // Lock while we check state. We must maintain the lock while adding the new pair so that
    // another thread can't run the list out from under us. We only add to the list if we have not
    // yet started execution.
    synchronized (this) {
      if (!executed) {

<img src="/img/tutorial/separate-openapi-schemas/image02.png">
</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

In this case, the original path `/app` would actually be served at `/api/v1/app`.

Even though all your code is written assuming there's just `/app`.

{* ../../docs_src/behind_a_proxy/tutorial001.py hl[6] *}

import com.google.common.collect.SortedSetMultimap;
import org.junit.Ignore;

/**
 * Tester for {@link SortedSetMultimap#get(Object)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

    Optional<String> z = Optional.of("z");

    Comparator<Optional<String>> comparator = emptiesFirst(comparing(String::length));
    testComparator(comparator, empty, z, abc);

    // Just demonstrate that no explicit type parameter is required
    Comparator<Optional<String>> unused = emptiesFirst(naturalOrder());
  }

  public void testEmptiesLast() {
    Optional<String> empty = Optional.empty();

    }

    // Test that close method exists (inherited)
    public void test_closeMethodExists() {
        // Test that close method is available (inherited from parent)
        try {
            // Just verify the method exists, don't actually call it
            crawlerEngineClient.getClass().getMethod("close");
            assertTrue(true);
        } catch (NoSuchMethodException e) {

        result *= i;
      }
      return BigInteger.valueOf(result);
    }

    /*
     * We want each multiplication to have both sides with approximately the same number of digits.
     * Currently, we just divide the range in half.
     */
    int mid = (n1 + n2) >>> 1;
    return oldSlowFactorial(n1, mid).multiply(oldSlowFactorial(mid, n2));
  }

  @Benchmark
  int slowFactorial(int reps) {
    int tmp = 0;

	if set {
		if err := setxattr(path, name, value); err != nil {
			log.Fatalln(fmt.Errorf("setting attribute %s failed with: %v", name, err))
		}
	} else {
		if name == "" {
			log.Fatalln("you must specify an attribute name for reading")
		}
		var names []string
		if name == "." {
			attrs, err := listxattr(path)
			if err != nil {
				log.Fatalln(fmt.Errorf("listing attributes failed with: %v", err))
			}