* of the supertype that suggests that implementations are expected to tolerate null. That said, I
   * see calls in Google code that pass a null `dir` to a FilenameFilter.... So let's declare the
   * parameter as non-nullable (since passing null to a FilenameFilter is unsafe in general), but if
   * someone still manages to pass null, let's continue to have the method work.
   *

  }

  /**
   * Wrapper for {@link Map#get(Object)} that forces the caller to pass in a key of the same type as
   * the map. Besides being slightly shorter than code that uses {@link #getMap()}, it also ensures
   * that callers don't pass an {@link Entry} by mistake.
   */
  protected V get(K key) {
    return getMap().get(key);
  }

  protected final K k0() {

    return delegate().apply(key);
  }

  @Override
  public void refresh(K key) {
    delegate().refresh(key);
  }

  /**
   * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
   * constructed {@link LoadingCache} as the delegate.
   *
   * @since 10.0
   */
  public abstract static class SimpleForwardingLoadingCache<K, V>
      extends ForwardingLoadingCache<K, V> {

  }

  /**
   * Returns a cache loader that uses {@code function} to load keys, and without supporting either
   * reloading or bulk loading. This is most useful when you can pass a lambda expression. Otherwise
   * it is useful mostly when you already have an existing function instance.
   *
   * <p>The returned object is serializable if {@code function} is serializable.
   *

   *       in the {@code exceptions} collection.
   * </ul>
   *
   * <p>Though this method takes any {@link Collection}, it often makes most sense to pass a {@link
   * java.util.List} or some other collection that preserves the order in which the exceptions got
   * added.
   *
   * @throws NullPointerException if {@code exceptions} is null

    Map<K, V> delegateMap = Maps.newHashMapWithExpectedSize(n);
    // If duplicates are allowed, this map will track the last value for each duplicated key.
    // A second pass will retain only the first entry for that key, but with this last value. The
    // value will then be replaced by null, signaling that later entries with the same key should
    // be deleted.

      fail("Trailing high surrogate should cause exception");
    } catch (IllegalArgumentException expected) {
      // Pass
    }
    try {
      escapeAsString(SIMPLE_ESCAPER, test);
      fail("Trailing high surrogate should cause exception");
    } catch (IllegalArgumentException expected) {
      // Pass
    }
  }

  public void testNullInput() {
    UnicodeEscaper e = SIMPLE_ESCAPER;
    try {

    } catch (IllegalArgumentException e) {
      // pass
    }
    assertEquals("<lo><hi>", charEscaper.escape("\uDC00\uD800"));
    try {
      unicodeEscaper.escape("\uDC00\uD800");
      fail("should have failed for bad Unicode input");
    } catch (IllegalArgumentException e) {
      // pass
    }
  }

  // A trivial non-optimized escaper for testing.

    // URL escapers should throw null pointer exceptions for null input
    try {
      e.escape((String) null);
      fail("Escaping null string should throw exception");
    } catch (NullPointerException x) {
      // pass
    }

    // All URL escapers should leave 0-9, A-Z, a-z unescaped
    assertUnescaped(e, 'a');
    assertUnescaped(e, 'z');
    assertUnescaped(e, 'A');
    assertUnescaped(e, 'Z');
    assertUnescaped(e, '0');

  public void testBadArguments_null() {
    try {
      new PercentEscaper(null, false);
      fail("Expected null pointer exception for null parameter");
    } catch (NullPointerException expected) {
      // pass
    }
  }

  /**
   * Tests that specifying any alphanumeric characters as 'safe' causes an {@link
   * IllegalArgumentException}.
   */
  public void testBadArguments_badchars() {
    String msg =