unfiltered,
            new Predicate<String>() {
              @Override
              public boolean apply(String s) {
                throw new AssertionFailedError("Should never be evaluated");
              }
            });

    List<String> expected = Collections.emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked")
  // unsafe, comparator() returns a comparator on the specified type
  // TODO(kevinb): evaluate whether or not of().comparator() should return null
  public static <K, V> ImmutableSortedMap<K, V> of() {
    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }

   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked")
  // unsafe, comparator() returns a comparator on the specified type
  // TODO(kevinb): evaluate whether or not of().comparator() should return null
  public static <K, V> ImmutableSortedMap<K, V> of() {
    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }

   * operations like {@link Multimap#containsValue} and {@code Multimap.toString()}. For this to
   * perform well, {@code function} should be fast. To avoid lazy evaluation when the returned
   * multimap doesn't need to be a view, copy the returned multimap into a new multimap of your
   * choosing.
   *
   * @since 7.0
   */
  public static <

            unfiltered,
            new Predicate<String>() {
              @Override
              public boolean apply(String s) {
                throw new AssertionFailedError("Should never be evaluated");
              }
            });

    List<String> expected = Collections.emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

   * transformation function.
   *
   * <p>The primary audience of this method is callers of {@code transform} who don't have a {@code
   * ListenableFuture} available and do not mind repeated, lazy function evaluation.
   *
   * @param input The future to transform
   * @param function A Function to transform the results of the provided future to the results of
   *     the returned future.