assertTrue(Integer.toHexString(c), whitespace().matches((char) c));
      }
    }
  }

  // The next tests require ICU4J and have, at least for now, been sliced out
  // of the open-source view of the tests.

  @J2ktIncompatible
  @GwtIncompatible // Character.isISOControl
  public void testJavaIsoControl() {
    for (int c = 0; c <= Character.MAX_VALUE; c++) {
      assertEquals(

{!> ../../docs_src/python_types/tutorial009b.py!}
```

////

#### Sử dụng `Union` hay `Optional`

If you are using a Python version below 3.10, here's a tip from my very **subjective** point of view:

Nếu bạn đang sử dụng phiên bản Python dưới 3.10, đây là một mẹo từ ý kiến rất "chủ quan" của tôi:

* 🚨 Tránh sử dụng `Optional[SomeType]`
* Thay vào đó ✨ **sử dụng `Union[SomeType, None]`** ✨.

  /**
   * Provides a snapshot of the current state of all the services under management.
   *
   * <p>N.B. This snapshot is guaranteed to be consistent, i.e. the set of states returned will
   * correspond to a point in time view of the services.
   *
   * @since 29.0 (present with return type {@code ImmutableMultimap} since 14.0)
   */
  @Override
  public ImmutableSetMultimap<State, Service> servicesByState() {

  /**
   * Provides a snapshot of the current state of all the services under management.
   *
   * <p>N.B. This snapshot is guaranteed to be consistent, i.e. the set of states returned will
   * correspond to a point in time view of the services.
   *
   * @since 29.0 (present with return type {@code ImmutableMultimap} since 14.0)
   */
  @Override
  public ImmutableSetMultimap<State, Service> servicesByState() {

    }

    private String getLocalizedPagePath(final String page, final String lang, final String country) {
        final StringBuilder buf = new StringBuilder(100);
        buf.append("/WEB-INF/view/").append(page);
        if (StringUtil.isNotBlank(lang)) {
            buf.append('_').append(lang);
            if (StringUtil.isNotBlank(country)) {
                buf.append('_').append(country);
            }

    TreeSet<Integer> mod = Sets.newTreeSet();
    mod.add(1);
    mod.add(2);
    mod.add(3);

    NavigableSet<Integer> unmod = unmodifiableNavigableSet(mod);

    /* Unmodifiable is a view. */
    mod.add(4);
    assertTrue(unmod.contains(4));
    assertTrue(unmod.descendingSet().contains(4));

    ensureNotDirectlyModifiable(unmod);
    ensureNotDirectlyModifiable(unmod.descendingSet());

   * the returned list is unspecified.
   *
   * <p>The returned list is serializable.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Character> asList(char... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new CharArrayAsList(backingArray);
  }

 *           }
 *         });
 * }</pre>
 *
 * <p>The returned cache implements all optional operations of the {@link LoadingCache} and {@link
 * Cache} interfaces. The {@code asMap} view (and its collection views) have <i>weakly consistent
 * iterators</i>. This means that they are safe for concurrent use, but if other threads modify the

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   * is used as a parameter to any of its methods.
   *
   * <p>The returned list is serializable.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Float> asList(float... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new FloatArrayAsList(backingArray);
  }