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

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

        return value;
    }

    /**
     * Extracts text content from a single node using XPath expression.
     *
     * @param document the parsed HTML document
     * @param xpath the XPath expression to evaluate
     * @param pruneFunc the function to apply for node pruning
     * @return the extracted text content
     */

   *
   * <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;
  }