*
     * @param artifact The artifact whose available versions should be determined, must not be {@code null}.
     * @return The available versions of the artifact or an empty list if none, never {@code null}.
     * @since 3.0-alpha-3
     */
    List<String> findVersions(Artifact artifact);

    /**

        }

        @Override
        public String[] getGroupNames() {
            return groups;
        }

        @Override
        public String[] getPermissions() {
            if (permissions == null) {
                final SystemHelper systemHelper = ComponentUtil.getSystemHelper();
                final Set<String> permissionSet = new HashSet<>();
                final UserInfo userInfo = authResult.getUserInfo();

    }

    protected void setupListCondition(final AccessTokenCB cb, final AccessTokenPager accessTokenPager) {
        if (accessTokenPager.id != null) {
            cb.query().docMeta().setId_Equal(accessTokenPager.id);
        }
        // TODO Long, Integer, String supported only.

        // setup condition
        cb.query().addOrderBy_Name_Asc();

                    return groovyShell.evaluate(template);
                } catch (final JobProcessingException e) {
                    throw e;
                } catch (final Exception e) {
                    return null;
                } finally {
                    final GroovyClassLoader loader = groovyShell.getClassLoader();
                    loader.clearCache();
                }
            }

            @Override

    boolean ran = false;
    @Nullable Callback callback = null;

    public SimpleTearDown() {}

    public SimpleTearDown(Callback callback) {
      this.callback = callback;
    }

    @Override
    public void tearDown() throws Exception {
      if (callback != null) {
        callback.run();
      }
      ran = true;
    }
  }

  fun value(index: Int): String = encodedValue(index).percentDecode(plusIsSpace = true)

  override fun contentType(): MediaType = CONTENT_TYPE

  override fun contentLength(): Long = writeOrCountBytes(null, true)

  @Throws(IOException::class)
  override fun writeTo(sink: BufferedSink) {
    writeOrCountBytes(sink, false)
  }

  /**

  }

  @Override
  @CheckForNull
  public Entry<E> firstEntry() {
    return isEmpty() ? null : getEntry(0);
  }

  @Override
  @CheckForNull
  public Entry<E> lastEntry() {
    return isEmpty() ? null : getEntry(length - 1);
  }

  @Override
  public int count(@CheckForNull Object element) {
    int index = elementSet.indexOf(element);

            String pluginId = mixin.getPluginId();
            ClassExtensionDoc classExtensionDoc = plugins.get(pluginId);
            if (classExtensionDoc == null) {
                classExtensionDoc = new ClassExtensionDoc(pluginId, classDoc);
                plugins.put(pluginId, classExtensionDoc);
            }

<div class="screenshot">
<img src="/img/tutorial/separate-openapi-schemas/image02.png">
</div>

Isso significa que ele **sempre terá um valor**, só que às vezes o valor pode ser `None` (ou `null` em termos de JSON).

    @CheckForNull
    private Iterator<? extends Iterator<? extends T>> getTopMetaIterator() {
      while (topMetaIterator == null || !topMetaIterator.hasNext()) {
        if (metaIterators != null && !metaIterators.isEmpty()) {
          topMetaIterator = metaIterators.removeFirst();
        } else {
          return null;
        }
      }