assertThat(union(emptySet(), emptySet()).immutableCopy()).isEmpty();
    assertThat(intersection(newHashSet(1, 2), newHashSet(3, 4)).immutableCopy()).isEmpty();
    assertThat(difference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
    assertThat(symmetricDifference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
  }

  public void testImmutableCopy() {

            buf.append(",\"related_contents\":");
            buf.append(escapeJson(relatedContents));
            buf.append(',');
            buf.append("\"data\":[");
            if (!documentItems.isEmpty()) {
                boolean first1 = true;
                for (final Map<String, Object> document : documentItems) {
                    if (!first1) {
                        buf.append(',');

      Multimap<? extends K, ? extends V> multimap,
      @Nullable Comparator<? super V> valueComparator) {
    checkNotNull(multimap); // eager for GWT
    if (multimap.isEmpty() && valueComparator == null) {
      return of();
    }

    if (multimap instanceof ImmutableSetMultimap) {
      @SuppressWarnings("unchecked") // safe since multimap is not writable

            }
        }

        public void removeChannel(ChannelInfo channel) {
            channels.remove(channel);
            if (primaryChannel == channel && !channels.isEmpty()) {
                primaryChannel = channels.get(0);
            }
        }

        public ChannelInfo getPrimaryChannel() {
            return primaryChannel;
        }

    public ImmutableBiMap<K, V> build() {
      return buildOrThrow();
    }

    @Override
    public ImmutableBiMap<K, V> buildOrThrow() {
      ImmutableMap<K, V> map = super.buildOrThrow();
      if (map.isEmpty()) {
        return of();
      }
      return new RegularImmutableBiMap<K, V>(super.buildOrThrow());
    }

    @Override
    ImmutableBiMap<K, V> buildJdkBacked() {
      return build();
    }

    @Override
    public Artifact createPluginArtifact(Plugin plugin) {
        VersionRange versionRange;
        try {
            String version = plugin.getVersion();
            if (version == null || version.isEmpty()) {
                version = "RELEASE";
            }
            versionRange = VersionRange.createFromVersionSpec(version);
        } catch (InvalidVersionSpecificationException e) {
            return null;

        }

        final Set<String> matchedLabelSet = ComponentUtil.getLabelTypeHelper().getMatchedLabelValueSet(url);
        if (!matchedLabelSet.isEmpty()) {
            final Set<String> newLabelSet = new HashSet<>();
            final String[] oldLabels = DocumentUtil.getValue(dataMap, fessConfig.getIndexFieldLabel(), String[].class);

        String response = checkGetMethod(searchBody, "").asString();
        final Map<String, Object> res = JsonPath.from(response).getMap("response.setting");
        assertTrue(!res.isEmpty());
        assertEquals(Integer.valueOf(0), JsonPath.from(response).get("response.status"));
    }

    @Override
    protected void tearDown() {
        // do nothing
    }

    @Test

  public void testEmptyMap() {
    Map<Character, String> map = ImmutableMap.of();
    ArrayBasedEscaperMap fem = ArrayBasedEscaperMap.create(map);
    // Non-null array of zero length.
    assertThat(fem.getReplacementArray()).isEmpty();
  }

  public void testMapLength() {
    Map<Character, String> map =
        ImmutableMap.of(
            'a', "first",
            'z', "last");

    protected boolean canDetectActivation(Profile profile) {
        return profile.getActivation() != null
                && profile.getActivation().getJdk() != null
                && !profile.getActivation().getJdk().isEmpty();
    }