* @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

    if (hasSameComparator && (elements instanceof ImmutableSortedSet)) {
      @SuppressWarnings("unchecked")
      ImmutableSortedSet<E> original = (ImmutableSortedSet<E>) elements;
      if (!original.isPartialView()) {
        return original;
      }
    }
    @SuppressWarnings("unchecked") // elements only contains E's; it's safe.
    E[] array = (E[]) Iterables.toArray(elements);

           * requireNonNull is safe because the first `2*(size+keyOffset)` elements have been filled
           * in.
           */
          @SuppressWarnings("unchecked")
          K key = (K) requireNonNull(alternatingKeysAndValues[2 * index + keyOffset]);
          @SuppressWarnings("unchecked")
          V value = (V) requireNonNull(alternatingKeysAndValues[2 * index + (keyOffset ^ 1)]);

    @CheckForNull
    public Collection<V> get(@CheckForNull Object key) {
      Collection<V> result = unfiltered.asMap().get(key);
      if (result == null) {
        return null;
      }
      @SuppressWarnings("unchecked") // key is equal to a K, if not a K itself
      K k = (K) key;
      result = filterCollection(result, new ValuePredicate(k));
      return result.isEmpty() ? null : result;
    }

    @Override

    }
  }

  @SuppressWarnings("unchecked") // C can only be @Nullable Character or Character
  protected @NonNull C cellValue(Character character) {
    return (C) character;
  }

  // Only safe wrt. ClassCastException. Not null-safe (can be used to test expected Table NPEs)
  @SuppressWarnings("unchecked")
  protected C nullableCellValue(@Nullable Character character) {

      @SuppressWarnings({"rawtypes", "unchecked"})
      Entry<Object, V>[] entries = new Entry[size];
      for (int i = 0; i < size; i++) {
        // requireNonNull is safe because the first `2*size` elements have been filled in.
        Object key = requireNonNull(alternatingKeysAndValues[2 * i]);
        @SuppressWarnings("unchecked")
        V value = (V) requireNonNull(alternatingKeysAndValues[2 * i + 1]);

import javax.annotation.CheckForNull;

/**
 * Unchecked variant of {@link java.util.concurrent.ExecutionException}. As with {@code
 * ExecutionException}, the exception's {@linkplain #getCause() cause} comes from a failed task,
 * possibly run in another thread.
 *
 * <p>{@code UncheckedExecutionException} is intended as an alternative to {@code
 * ExecutionException} when the exception thrown by a task is an unchecked exception. However, it

                require(diagnostic is DiagnosticWithParameters1<*, *>)
                @Suppress("UNCHECKED_CAST")
                diagnostic.a as Collection<ResolvedCall<*>>
            }
            in diagnosticWithResolvedCallsAtPosition2 -> {
                require(diagnostic is DiagnosticWithParameters2<*, *, *>)
                @Suppress("UNCHECKED_CAST")
                diagnostic.b as Collection<ResolvedCall<*>>
            }

    @Test
    public void testPluginArtifactsExpressionReference() throws Exception {
        Session session = newSession();
        MojoExecution exec = newMojoExecution(session);

        @SuppressWarnings("unchecked")
        Collection<Artifact> depResults = (Collection<Artifact>)
                new PluginParameterExpressionEvaluatorV4(session, null, exec).evaluate("${mojo.plugin.dependencies}");

    /**
     *
     */
    @Test
    public void test() {
        final List<String> list1 = asList("Foo", "Bar");
        final List<String> list2 = asList("Baz");

        @SuppressWarnings("unchecked")
        final Iterator<String> it = new MultiIterator<String>(list1.iterator(), list2.iterator());

        assertThat(it.hasNext(), is(true));
        assertThat(it.next(), is("Foo"));