return null;
        }

        @Override
        public int size() {
          return 0;
        }

        @Override
        public Iterator<Object> iterator() {
          return ImmutableSet.of().iterator();
        }
      };

  /** Queue that discards all elements. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value

    assertNotified(listener, two, three, RemovalCause.EXPLICIT);

    map.put(three, four);
    Iterator<?> i = map.entrySet().iterator();
    i.next();
    i.remove();
    assertNotified(listener, three, four, RemovalCause.EXPLICIT);

    map.put(four, five);
    i = map.keySet().iterator();
    i.next();
    i.remove();
    assertNotified(listener, four, five, RemovalCause.EXPLICIT);

    assertNotified(listener, two, three, RemovalCause.EXPLICIT);

    map.put(three, four);
    Iterator<?> i = map.entrySet().iterator();
    i.next();
    i.remove();
    assertNotified(listener, three, four, RemovalCause.EXPLICIT);

    map.put(four, five);
    i = map.keySet().iterator();
    i.next();
    i.remove();
    assertNotified(listener, four, five, RemovalCause.EXPLICIT);

    }

    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return Iterators.filter(unfiltered.entrySet().iterator(), entryPredicate);
    }

    @Override
    Iterator<Entry<K, V>> descendingEntryIterator() {
      return Iterators.filter(unfiltered.descendingMap().entrySet().iterator(), entryPredicate);
    }

    @Override
    public int size() {

          return null;
        }

        @Override
        public int size() {
          return 0;
        }

        @Override
        public Iterator<Object> iterator() {
          return ImmutableSet.of().iterator();
        }
      };

  /** Queue that discards all elements. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value

   * An object that holds the final result of an asynchronous {@link ClosingFuture} operation and
   * allows the user to close all the closeable objects that were captured during it for later
   * closing.
   *
   * <p>The asynchronous operation will have completed before this object is created.
   *
   * @param <V> the type of the value of a successful operation
   * @see ClosingFuture#finishToValueAndCloser(ValueAndCloserConsumer, Executor)