this.queue = checkNotNull(queue);
  }

  @Override
  protected @Nullable T computeNext() {
    // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
    if (queue.isEmpty()) {
      return endOfData();
    }
    return queue.remove();
  }

            final Map<String, String[]> fields = parseFieldFilters(request);
            final String[] extraQueries = parseExtraQueries(request);
            final ChatResult result;
            if (fields.isEmpty() && extraQueries.length == 0) {
                result = ComponentUtil.getChatClient().chat(sessionId, message, userId);
            } else {

	if !found {
		// Check for sub-prefix only if the input value is only a
		// single value, this rejects invalid inputs if any.
		found = !SubSystems.FuncMatch(strings.HasPrefix, subSystemValue[0]).IsEmpty() && len(subSystemValue) == 1
	}
	if !found {
		return nil, Errorf("unknown sub-system %s", s)
	}

	targets := Targets{}
	subSysPrefix := subSystemValue[0]
	if len(subSystemValue) == 2 {

    @Override
    protected SortedSet<Integer> create(Integer[] elements) {
      SortedSet<Integer> set = nullCheckedTreeSet(elements);
      int tooHigh = set.isEmpty() ? 0 : set.last() + 1;
      set.add(tooHigh);
      return checkedCreate(set).headSet(tooHigh);
    }
  }

  public static class ContiguousSetTailsetGenerator extends AbstractContiguousSetGenerator {

        Set<ApiChange> seenApiChanges = (Set<ApiChange>) context.getUserData().get("seenApiChanges");
        Set<ApiChange> left = new HashSet<>(acceptedApiChanges);
        left.removeAll(seenApiChanges);
        if (!left.isEmpty()) {
            String formattedLeft = CollectionUtils.join("\n", left);
            throw new RuntimeException("The following regressions are declared as accepted, but didn't match any rule:\n\n" + formattedLeft);
        }

  @Throws(InterruptedException::class)
  fun takeSink(): BufferedSink = requestBodySinks.poll(5, SECONDS) ?: throw AssertionError("no sink to take")

  fun assertNoMoreSinks() {
    assertTrue(requestBodySinks.isEmpty())
  }

    PreOrderIterator(T root) {
      this.stack = new ArrayDeque<>();
      stack.addLast(singletonIterator(checkNotNull(root)));
    }

    @Override
    public boolean hasNext() {
      return !stack.isEmpty();
    }

    @Override
    public T next() {
      Iterator<T> itr = stack.getLast(); // throws NSEE if empty
      T result = checkNotNull(itr.next());
      if (!itr.hasNext()) {

  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonMapPollFirst() {
    assertEquals(a, navigableMap.pollFirstEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {
    assertNull(navigableMap.lowerEntry(k0()));
    assertNull(navigableMap.lowerKey(k0()));

  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonSetPollFirst() {
    assertEquals(a, navigableSet.pollFirst());
    assertTrue(navigableSet.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonSetNearby() {
    assertNull(navigableSet.lower(e0()));
    assertEquals(a, navigableSet.floor(e0()));

  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonMapPollFirst() {
    assertEquals(a, navigableMap.pollFirstEntry());
    assertTrue(navigableMap.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapNearby() {
    assertNull(navigableMap.lowerEntry(k0()));
    assertNull(navigableMap.lowerKey(k0()));