*     string using {@link String#valueOf(Object)}
   * @throws IllegalArgumentException if {@code expression} is false
   */
  public static void checkArgument(boolean expression, @CheckForNull Object errorMessage) {
    if (!expression) {
      throw new IllegalArgumentException(String.valueOf(errorMessage));
    }
  }

  /**

            new Function<String, Integer>() {
              @Override
              public Integer apply(String from) {
                return Integer.valueOf(from);
              }
            });

    assertEquals(Integer.valueOf(1), iterator.next());
    assertEquals(Integer.valueOf(2), iterator.next());
    iterator.remove();
    assertEquals(asList("1", "3"), list);
  }

  public void testPoorlyBehavedTransform() {

    assertEquals(Integer.valueOf(4), map.get("four"));
  }

  public void testAsMapWritesThrough() {
    Set<String> strings = Sets.newLinkedHashSet();
    Collections.addAll(strings, "one", "two", "three");
    Map<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);
    assertEquals(ImmutableMap.of("one", 3, "two", 3, "three", 5), map);
    assertEquals(Integer.valueOf(3), map.remove("two"));

    assertEquals(Integer.valueOf(4), map.get("four"));
  }

  public void testAsMapWritesThrough() {
    Set<String> strings = Sets.newLinkedHashSet();
    Collections.addAll(strings, "one", "two", "three");
    Map<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);
    assertEquals(ImmutableMap.of("one", 3, "two", 3, "three", 5), map);
    assertEquals(Integer.valueOf(3), map.remove("two"));

   *     string using {@link String#valueOf(Object)}
   * @throws IllegalArgumentException if {@code expression} is false
   */
  public static void checkArgument(boolean expression, @CheckForNull Object errorMessage) {
    if (!expression) {
      throw new IllegalArgumentException(String.valueOf(errorMessage));
    }
  }

  /**

            new Function<String, Integer>() {
              @Override
              public Integer apply(String from) {
                return Integer.valueOf(from);
              }
            });

    assertEquals(Integer.valueOf(1), iterator.next());
    assertEquals(Integer.valueOf(2), iterator.next());
    iterator.remove();
    assertEquals(asList("1", "3"), list);
  }

  public void testPoorlyBehavedTransform() {

      }
      return result.toString();
    }

    @Override
    public String collapseFrom(CharSequence sequence, char replacement) {
      return (sequence.length() == 0) ? "" : String.valueOf(replacement);
    }

    @Override
    public String trimFrom(CharSequence sequence) {
      checkNotNull(sequence);
      return "";
    }

    @Override

      }
      return result.toString();
    }

    @Override
    public String collapseFrom(CharSequence sequence, char replacement) {
      return (sequence.length() == 0) ? "" : String.valueOf(replacement);
    }

    @Override
    public String trimFrom(CharSequence sequence) {
      checkNotNull(sequence);
      return "";
    }

    @Override