return (result == null) ? elementSet = new ElementSet() : result;
  }

  @WeakOuter
  private final class ElementSet extends IndexedImmutableSet<E> {

    @Override
    E get(int index) {
      return contents.getKey(index);
    }

    @Override
    public boolean contains(@Nullable Object object) {
      return RegularImmutableMultiset.this.contains(object);
    }

    @Override
    boolean isPartialView() {

     */
    public void flushPluginMap() {
    }

    /**
     * @return a Map of plugins field with {@code Plugins#getKey()} as key
     * @see Plugin#getKey()
     */
    public Map<String, Plugin> getPluginsAsMap() {
        return getPlugins().stream().collect(Collectors.toMap(plugin -> plugin.getKey(), plugin -> plugin));
    }
            ]]>
          </code>
        </codeSegment>
        <codeSegment>

            new TestStringMapGenerator() {
              @Override
              protected Map<String, String> create(Entry<String, String>[] entries) {
                return singletonMap(entries[0].getKey(), entries[0].getValue());
              }
            })
        .named("singletonMap")
        .withFeatures(
            MapFeature.ALLOWS_NULL_KEYS,
            MapFeature.ALLOWS_NULL_VALUES,

        "Should not contain null after unsupported putIfAbsent(present, null)");
  }

  @CanIgnoreReturnValue
  private V putIfAbsent(Entry<K, V> entry) {
    return getMap().putIfAbsent(entry.getKey(), entry.getValue());
  }

  public void testPut_nullValueSupported() {
    Entry<K, V> nullValueEntry = entry(k3(), null);
    assertNull(
        "putIfAbsent(key, null) should return null",
        getMap().putIfAbsent(nullValueEntry.getKey(), nullValueEntry.getValue()));
    expectAdded(nullValueEntry);
  }

    void setReleaseUpdatePolicy(ArtifactRepositoryPolicy policy);

    ArtifactRepositoryLayout getLayout();

    void setLayout(ArtifactRepositoryLayout layout);

    String getKey();

    @Deprecated
    boolean isUniqueVersion();

    @Deprecated
    boolean isBlacklisted();

    @Deprecated
    void setBlacklisted(boolean blackListed);

    /**

    assertNull("put(null, null) should return null", put(nullKeyValueEntry));
    expectAdded(nullKeyValueEntry);
  }

  @CanIgnoreReturnValue
  private V put(Entry<K, V> entry) {
    return getMap().put(entry.getKey(), entry.getValue());
  }

  /**
   * Returns the {@link Method} instance for {@link #testPut_nullKeyUnsupported()} so that tests of
   * {@link java.util.TreeMap} can suppress it with {@code

                                                                logger.debug("Skipping interpolation of field: " + field
                                                                        + " (key: " + entry.getKey() + ") in: "
                                                                        + cls.getName()
                                                                        + "; it is an unmodifiable collection.");

        this.link = link;
    }

    /**
     * @return the key
     */
    @Override
    public String getKey() {
        return this.key;
    }

    /**
     * @param key
     *            the key to set
     */
    @Override
    public void setKey(final String key) {
        this.key = key;
    }

    @Override
    public String getServer() {

        if (headers != null) {
            // Mock by header name
            for (Map.Entry<String, List<String>> entry : headers.entrySet()) {
                when(conn.getHeaderField(entry.getKey())).thenReturn(entry.getValue().get(0));
            }

            // Mock by index - getHeaderField(int)
            // Index 0 is status line, then headers in order
            int index = 1;