public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector<@Nullable Object, ?, @Nullable Object> ONLY_ELEMENT =
      Collector.<@Nullable Object, ToOptionalState, @Nullable Object>of(
          ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),

  }

  /**
   * A sensible definition of {@link #subMultiset(Object, BoundType, Object, BoundType)} in terms of
   * {@link #headMultiset(Object, BoundType) headMultiset} and {@link #tailMultiset(Object,
   * BoundType) tailMultiset}.
   *
   * <p>If you override either of these methods, you may wish to override {@link
   * #subMultiset(Object, BoundType, Object, BoundType)} to forward to this implementation.
   */

  abstract static class SuperClass {
    public abstract void overriddenInSubclassNowhereAnnotated(Object o);

    public abstract void overriddenAndAnnotatedInSubclass(Object o);
  }

  static class SubClass extends SuperClass {
    final List<Object> overriddenInSubclassNowhereAnnotatedEvents = new ArrayList<>();
    final List<Object> overriddenAndAnnotatedInSubclassEvents = new ArrayList<>();

    @Override

   * @return the stripes corresponding to the objects (one per each object, derived by delegating to
   *     {@link #get(Object)}; may contain duplicates), in an increasing index order.
   */
  public Iterable<L> bulkGet(Iterable<? extends Object> keys) {
    // Initially using the list to store the keys, then reusing it to store the respective L's
    List<Object> result = newArrayList(keys);
    if (result.isEmpty()) {

  }

  private static <E extends @Nullable Object> void assertCollectionsAreEquivalent(
      Collection<E> expected, Collection<E> actual) {
    assertIteratorsInOrder(expected.iterator(), actual.iterator());
  }

  private static <K extends @Nullable Object, V extends @Nullable Object>
      void assertMultimapRemainsUnmodified(Multimap<K, V> expected, List<Entry<K, V>> actual) {

        return headerList;
    }

    public void addField(final String key, final Object value) {
        fields.put(key, value);
    }

    public String getLogMessage() {
        return getSearchWord();
    }

    @Override
    public Map<String, Object> toSource() {
        final Map<String, Object> sourceMap = super.toSource();
        if (fields != null) {
            sourceMap.putAll(fields);

   *
   * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**
   * Returns the hash code for this network. The hash code of a network is defined as the hash code
   * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object)
   * incident nodes}.
   *

   * {@link #valueField} of {@code future}.
   */
  static boolean casValue(AbstractFutureState<?> future, @Nullable Object expect, Object update) {
    return ATOMIC_HELPER.casValue(future, expect, update);
  }

  /** Returns the value of the future, using a volatile read. */
  final @Nullable Object value() {
    return valueField;
  }

  /** Returns the head of the listener stack, using a volatile read. */

      standardClear();
    }

    @Override
    public boolean contains(Object object) {
      return standardContains(object);
    }

    @Override
    public boolean containsAll(Collection<?> collection) {
      return standardContainsAll(collection);
    }

    @Override
    public boolean remove(Object object) {
      return standardRemove(object);
    }

    @Override

import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Objects;
import org.jspecify.annotations.Nullable;

/**
 * Implementation for {@link FilteredMultimap#values()}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
final class FilteredMultimapValues<K extends @Nullable Object, V extends @Nullable Object>
    extends AbstractCollection<V> {
  @Weak private final FilteredMultimap<K, V> multimap;