* value is undefined.
     *
     * @return The location of the problem, never {@code null}.
     */
    String getLocation();

    /**
     * Gets the exception that caused this problem (if any).
     *
     * @return The exception that caused this problem or {@code null} if not applicable.
     */
    Exception getException();

    /**
     * Gets the message that describes this problem.

        for (Vertex v : children) {
            DfsState state = stateMap.putIfAbsent(v, DfsState.VISITING);
            if (state == null) {
                cycle.addLast(v.label);
                List<String> ret = visitCycle(v.children, stateMap, cycle);
                if (ret != null) {
                    return ret;
                }
                cycle.removeLast();
                stateMap.put(v, DfsState.VISITED);

    }

    public static UrlQueue<?> getUrlQueue() {
        return URL_QUEUE_THREAD_LOCAL.get();
    }

    public static void setUrlQueue(final UrlQueue<?> urlQueue) {
        if (urlQueue == null) {
            URL_QUEUE_THREAD_LOCAL.remove();
        } else {
            URL_QUEUE_THREAD_LOCAL.set(urlQueue);
        }
    }

    public static CrawlerContext getCrawlerContext() {

            try {
                final StatsObject data = statsCache.getIfPresent(key);
                if (data != null && data.decrement() <= 0) {
                    statsCache.invalidate(key);
                    final Long begin = data.remove(BEGIN_KEY);
                    if (begin != null) {
                        printStats(keyObj, data, begin, true);
                    }
                }

    // manually add elements to avoid expansion
    // 1/3 null keys, 1/3 null values
    int originalCount = 1024;
    InternalEntry<Object, Object, ?> entry = null;
    for (int i = 0; i < originalCount; i++) {
      Object key = new Object();
      Object value = (i % 3 == 0) ? null : new Object();
      int hash = map.hash(key);
      if (i % 3 == 1) {
        key = null;
      }

    // manually add elements to avoid expansion
    // 1/3 null keys, 1/3 null values
    int originalCount = 1024;
    InternalEntry<Object, Object, ?> entry = null;
    for (int i = 0; i < originalCount; i++) {
      Object key = new Object();
      Object value = (i % 3 == 0) ? null : new Object();
      int hash = map.hash(key);
      if (i % 3 == 1) {
        key = null;
      }

                .source(nonNull(source, "source cannot be null"))
                .build();
    }

    @Nonnull
    static ProjectBuilderRequest build(@Nonnull Session session, @Nonnull Path path) {
        return builder()
                .session(nonNull(session, "session cannot be null"))
                .path(nonNull(path, "path cannot be null"))
                .build();
    }

    @Execute
    public HtmlResponse index() {
        getSession().ifPresent(session -> session.removeAttribute(INVALID_OLD_PASSWORD));
        return asIndexPage(null).useForm(LoginForm.class);
    }

    private HtmlResponse asIndexPage(final LoginForm form) {
        if (form != null) {
            form.clearSecurityInfo();
        }
        return asHtml(virtualHost(path_Login_IndexJsp)).renderWith(data -> {

      return;
    }

    map.put(null, unmappedValue);
    assertEquals(unmappedValue, map.get(null));
    assertTrue(map.containsKey(null));
    Entry<@Nullable K, V> entry = mapEntry(null, unmappedValue);
    assertTrue(entrySet.remove(entry));
    assertNull(map.get(null));
    assertFalse(map.containsKey(null));
  }

  public void testEntrySetRemoveNullKeyMissing() {

        existPrePage = false;
        existNextPage = false;
        pageSize = getDefaultPageSize();
        currentPageNumber = getDefaultCurrentPageNumber();

        id = null;
        name = null;
        versionNo = null;

    }

    protected int getDefaultCurrentPageNumber() {
        return DEFAULT_CURRENT_PAGE_NUMBER;
    }

    public int getAllRecordCount() {
        return allRecordCount;