toImmutableEnumMap(Entry::getKey, Entry::getValue);
    assertThrows(
        IllegalArgumentException.class,
        () -> Stream.of(mapEntry(AnEnum.A, 1), mapEntry(AnEnum.A, 11)).collect(collector));
  }

  public void testToImmutableMapMerging() {
    Collector<Entry<AnEnum, Integer>, ?, ImmutableMap<AnEnum, Integer>> collector =
        toImmutableEnumMap(Entry::getKey, Entry::getValue, Integer::sum);

Ich denke, `Union[SomeType, None]` ist expliziter bezüglich seiner Bedeutung.

Es geht nur um Wörter und Namen. Aber diese Worte können beeinflussen, wie Sie und Ihre Teamkollegen über den Code denken.

Nehmen wir zum Beispiel diese Funktion:

{* ../../docs_src/python_types/tutorial009c.py hl[1,4] *}

    Object key = new Object();
    assertSame(computed, cache.getUnchecked(key));
    RemovalNotification<Object, Object> notification = listener.remove();
    assertSame(key, notification.getKey());
    assertSame(computed, notification.getValue());
    assertSame(RemovalCause.SIZE, notification.getCause());
    assertTrue(listener.isEmpty());
    checkEmpty(cache);
  }

    Object key = new Object();
    assertSame(computed, cache.getUnchecked(key));
    RemovalNotification<Object, Object> notification = listener.remove();
    assertSame(key, notification.getKey());
    assertSame(computed, notification.getValue());
    assertSame(RemovalCause.SIZE, notification.getCause());
    assertTrue(listener.isEmpty());
    checkEmpty(cache);
  }

        return true;
    }

    @Override
    public String getBaseVersion() {
        return artifact.getBaseVersion();
    }

    @Override
    public Object getKey() {
        return "project " + artifact.getGroupId() + ":" + artifact.getArtifactId();
    }

    @Override
    public void merge(ArtifactMetadata metadata) {

            result.setName(DfTypeUtil.toString(source.get("name")));
            result.setAttributes(source.entrySet()
                    .stream()
                    .filter(e -> !"name".equals(e.getKey()))
                    .map(e -> new Pair<>(e.getKey(), (String) e.getValue()))
                    .collect(Collectors.toMap(Pair::getFirst, Pair::getSecond)));
            return result;

  protected final void assertMoreInvariants(Map<K, V> map) {
    BiMap<K, V> bimap = (BiMap<K, V>) map;

    for (Entry<K, V> entry : map.entrySet()) {
      assertEquals(entry.getKey() + "=" + entry.getValue(), entry.toString());
      assertEquals(entry.getKey(), bimap.inverse().get(entry.getValue()));
    }

    assertEquals("{" + JOINER.join(map.entrySet()) + "}", map.toString());

        for (final Map.Entry<Object, Object> entry : systemProperties.entrySet()) {
            if (isBugReportTarget(entry.getKey())) {
                itemList.add(createItem(entry.getKey(), entry.getValue()));
            }
        }

        return itemList;
    }

    /**
     * Checks if a property should be included in bug reports.
     *

      rowBuilder.put(row.getKey(), ImmutableMap.copyOf(row.getValue()));
    }
    this.rowMap = rowBuilder.buildOrThrow();

    ImmutableMap.Builder<C, ImmutableMap<R, V>> columnBuilder =
        new ImmutableMap.Builder<>(columns.size());
    for (Entry<C, Map<R, V>> col : columns.entrySet()) {
      columnBuilder.put(col.getKey(), ImmutableMap.copyOf(col.getValue()));
    }

    }

    @Override
    public ArtifactRepositoryPolicy getSnapshots() {
        return userLocalArtifactRepository.getSnapshots();
    }

    @Override
    public String getKey() {
        return userLocalArtifactRepository.getKey();
    }

    @Override
    public String getUrl() {
        return userLocalArtifactRepository.getUrl();
    }

    @Override
    public int hashCode() {