* <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
   * comparison to determine equality of values. This technically violates the specifications of the
   * methods {@link Map#containsValue containsValue}, {@link ConcurrentMap#remove(Object, Object)
   * remove(Object, Object)} and {@link ConcurrentMap#replace(Object, Object, Object) replace(K, V,
   * V)}, and may not be what you expect.
   *

    }

    @Override
    public boolean containsKey(final Object key) {
        return getProperties().containsKey(key);
    }

    @Override
    public boolean containsValue(final Object value) {
        return getProperties().containsValue(value);
    }

    @Override
    public Enumeration<Object> elements() {
        return getProperties().elements();
    }

    @Override

   */
  ALLOWS_NULL_KEY_QUERIES,
  ALLOWS_NULL_KEYS(ALLOWS_NULL_KEY_QUERIES),
  /**
   * The map does not throw {@code NullPointerException} on calls such as {@code
   * containsValue(null)}, {@code values().contains(null)} or {@code values().remove(null)}.
   */
  ALLOWS_NULL_VALUE_QUERIES,
  ALLOWS_NULL_VALUES(ALLOWS_NULL_VALUE_QUERIES),
  /**

    Multimap<String, Integer> multimap = createMultimap();
    assertTrue(multimap.containsKey("foo"));
    assertFalse(multimap.containsKey("cat"));
    assertTrue(multimap.containsValue(1));
    assertFalse(multimap.containsValue(5));
    assertTrue(multimap.containsEntry("foo", 1));
    assertFalse(multimap.containsEntry("cat", 1));
    assertFalse(multimap.containsEntry("foo", 5));

    Multimap<String, Integer> multimap = createMultimap();
    assertTrue(multimap.containsKey("foo"));
    assertFalse(multimap.containsKey("cat"));
    assertTrue(multimap.containsValue(1));
    assertFalse(multimap.containsValue(5));
    assertTrue(multimap.containsEntry("foo", 1));
    assertFalse(multimap.containsEntry("cat", 1));
    assertFalse(multimap.containsEntry("foo", 5));

    Multimap<String, Integer> multimap = createMultimap();
    assertTrue(multimap.containsKey("foo"));
    assertFalse(multimap.containsKey("cat"));
    assertTrue(multimap.containsValue(1));
    assertFalse(multimap.containsValue(5));
    assertTrue(multimap.containsEntry("foo", 1));
    assertFalse(multimap.containsEntry("cat", 1));
    assertFalse(multimap.containsEntry("foo", 5));

    return null;
  }

  @Override
  public boolean containsKey(Object key) {
    return cachingHashMap.containsKey(key) && !isExpired(cachingHashMap.get(key));
  }

  @Override
  public boolean containsValue(Object value) {
    for (Timestamped<V> val : cachingHashMap.values()) {
      if (val.getValue().equals(value)) {
        if (!isExpired(val)) {
          return true;
        }
      }
    }

      return backingSortedMap;
    }

    @Override
    public boolean containsKey(Object key) {
      return standardContainsKey(key);
    }

    @Override
    public boolean containsValue(Object value) {
      return standardContainsValue(value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> map) {
      standardPutAll(map);
    }

    @Override

  }

  // accessors

  @Override
  public boolean containsKey(@Nullable Object key) {
    return map.containsKey(key);
  }

  @Override
  public boolean containsValue(@Nullable Object value) {
    return value != null && super.containsValue(value);
  }

  @Override
  public int size() {
    return size;
  }

  // views

  /**

      return backingMap;
    }

    @Override
    public boolean containsKey(Object key) {
      return standardContainsKey(key);
    }

    @Override
    public boolean containsValue(Object value) {
      return standardContainsValue(value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> map) {
      standardPutAll(map);
    }

    @Override