List<@Nullable String> list = newArrayList("a", null, "b", null, "a", null);
    assertEquals(2, Iterators.frequency(list.iterator(), "a"));
    assertEquals(1, Iterators.frequency(list.iterator(), "b"));
    assertEquals(0, Iterators.frequency(list.iterator(), "c"));
    assertEquals(0, Iterators.frequency(list.iterator(), 4.2));
    assertEquals(3, Iterators.frequency(list.iterator(), null));
  }

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

   *
   * @throws NullPointerException if any key or value in {@code map} is null
   */
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSortedMap<K, V> copyOfSorted(SortedMap<K, ? extends V> map) {
    Comparator<? super K> comparator = map.comparator();
    if (comparator == null) {
      // If map has a null comparator, the keys should have a natural ordering,

        String groupId = model.getGroupId();
        if (groupId == null && model.getParent() != null) {
            groupId = model.getParent().getGroupId();
        }
        return groupId;
    }

    private String getVersion(Model model) {
        String version = model.getVersion();
        if (version == null && model.getParent() != null) {
            version = model.getParent().getVersion();
        }

                        prefix + prefix2 + "(groupId:artifactId)",
                        null,
                        "groupId of a plugin must be defined. ",
                        plugin);
            }

            if (plugin.getArtifactId() == null
                    || (plugin.getArtifactId() != null
                            && plugin.getArtifactId().trim().isEmpty())) {
                addViolation(

    override val element: KtUserType,
    val shortenedRef: String? = null,
    override val nameToImport: FqName? = null,
    override val importAllInParent: Boolean = false,
) : ElementToShorten()

private class ShortenQualifier(
    override val element: KtDotQualifiedExpression,
    val shortenedRef: String? = null,
    override val nameToImport: FqName? = null,
    override val importAllInParent: Boolean = false

                MavenProject project = request.getProject();

                List<ModelProblem> modelProblems = null;
                Throwable error = null;

                if (project == null) {
                    project = new MavenProject();
                    project.setFile(pomFile != null ? pomFile.toFile() : null);

                    ModelBuildingListener listener =

        if (psiElement !is KtExpression) return null
        if (firElement !is FirResolvedQualifier) return null

        val call = psiElement.getPossiblyQualifiedCallExpression() ?: return null
        if (call.typeArgumentList == null || call.valueArgumentList != null) return null

        val parentReferenceExpression = psiElement.parent as? KtDoubleColonExpression ?: return null

    }
  }

  /*
   * Preconditions.checkNotNull is *intended* for performing eager null checks on parameters that a
   * nullness checker can already "prove" are non-null. That means that the first parameter to
   * checkNotNull *should* be annotated to require it to be non-null.
   *
   * However, for a variety of reasons, Google developers have written a ton of code over the past

    node.thread = null; // mark as 'deleted'
    restart:
    while (true) {
      Waiter pred = null;
      Waiter curr = waiters;
      if (curr == Waiter.TOMBSTONE) {
        return; // give up if someone is calling complete
      }
      Waiter succ;
      while (curr != null) {
        succ = curr.next;
        if (curr.thread != null) { // we aren't unlinking this node, update pred.