assertMultimapRemainsUnmodified(multimap, originalEntries);

    // Test #keySet()
    assertSetIsUnmodifiable(multimap.keySet(), sampleKey);
    assertMultimapRemainsUnmodified(multimap, originalEntries);

    // Test #get()
    if (!multimap.isEmpty()) {
      K key = multimap.keySet().iterator().next();
      assertCollectionIsUnmodifiable(multimap.get(key), sampleValue);

      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public Set<K> keySet() {
      synchronized (mutex) {
        if (keySet == null) {
          keySet = typePreservingSet(delegate().keySet(), mutex);
        }
        return keySet;
      }
    }

    @Override
    public Collection<V> values() {
      synchronized (mutex) {

      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public Set<K> keySet() {
      synchronized (mutex) {
        if (keySet == null) {
          keySet = typePreservingSet(delegate().keySet(), mutex);
        }
        return keySet;
      }
    }

    @Override
    public Collection<V> values() {
      synchronized (mutex) {

     *
     * @param cmdList the command list to add properties to
     */
    protected void addFessConfigProperties(final List<String> cmdList) {
        System.getProperties()
                .keySet()
                .stream()
                .filter(k -> k != null && k.toString().startsWith(Constants.FESS_CONFIG_PREFIX))
                .forEach(k -> addSystemProperty(cmdList, k.toString(), null, null));
    }

      Set<K> keySet = new HashSet<>();
      List<Entry<K, V>> builder = new ArrayList<>();
      for (Object o : elements) {
        Entry<?, ?> entry = (Entry<?, ?>) o;
        // These come from Entry<K, Collection<V>>> objects somewhere.
        @SuppressWarnings("unchecked")
        K key = (K) entry.getKey();
        keySet.add(key);

    // Tests that serializing a map, its keySet, and values only writes the underlying data once.

    Object[] entries = new Object[2000];
    for (int i = 0; i < entries.length; i++) {
      entries[i] = i;
    }

    ImmutableMap<Integer, Integer> map = RegularImmutableMap.create(entries.length / 2, entries);
    Set<Integer> keySet = map.keySet();
    Collection<Integer> values = map.values();

  }

  @Override
  public Set<N> successors() {
    return adjacentNodes();
  }

  @Override
  public Set<E> incidentEdges() {
    return Collections.unmodifiableSet(incidentEdgeMap.keySet());
  }

  @Override
  public Set<E> inEdges() {
    return incidentEdges();
  }

  @Override
  public Set<E> outEdges() {
    return incidentEdges();
  }

  @Override

@GwtCompatible
public enum MapFeature implements Feature<Map> {
  /**
   * The map does not throw {@code NullPointerException} on calls such as {@code containsKey(null)},
   * {@code get(null)}, {@code keySet().contains(null)} or {@code remove(null)}.
   */
  ALLOWS_NULL_KEY_QUERIES,
  ALLOWS_NULL_KEYS(ALLOWS_NULL_KEY_QUERIES),
  /**
   * The map does not throw {@code NullPointerException} on calls such as {@code

      String value2 = key2.toString();
      assertThat(cache.getUnchecked(key1)).isSameInstanceAs(value1);
      assertThat(cache.getUnchecked(key2)).isSameInstanceAs(value2);
      assertThat(cache.asMap().keySet()).isEqualTo(ImmutableSet.of(key1, key2));
      assertThat(cache.asMap().values()).containsExactly(value1, value2);
      assertThat(cache.asMap().entrySet())

    assertMultimapRemainsUnmodified(multimap, originalEntries);

    // Test #keySet()
    assertSetIsUnmodifiable(multimap.keySet(), sampleKey);
    assertMultimapRemainsUnmodified(multimap, originalEntries);

    // Test #get()
    if (!multimap.isEmpty()) {
      K key = multimap.keySet().iterator().next();
      assertCollectionIsUnmodifiable(multimap.get(key), sampleValue);