*/
  public static <A extends @Nullable Object, B extends @Nullable Object, C extends @Nullable Object>
      Function<A, C> compose(Function<B, C> g, Function<A, ? extends B> f) {
    return new FunctionComposition<>(g, f);
  }

  private static final class FunctionComposition<
          A extends @Nullable Object, B extends @Nullable Object, C extends @Nullable Object>
      implements Function<A, C>, Serializable {

  }

  /**
   * Class for testing all permutations of nullable/non-nullable two-argument methods using
   * testMethod().
   *
   * <ul>
   *   <li>normalNormal: two params, neither is Nullable
   *   <li>nullableNormal: only first param is Nullable
   *   <li>normalNullable: only second param is Nullable
   *   <li>nullableNullable: both params are Nullable
   * </ul>
   */
  public static class TwoArg {

    }
  }

  private static <E extends @Nullable Object> E getElementOrThrow(@Nullable Entry<E> entry) {
    if (entry == null) {
      throw new NoSuchElementException();
    }
    return entry.getElement();
  }

  private static <E extends @Nullable Object> @Nullable E getElementOrNull(
      @Nullable Entry<E> entry) {
    return (entry == null) ? null : entry.getElement();
  }

@GwtIncompatible
public abstract class ForwardingNavigableMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingSortedMap<K, V> implements NavigableMap<K, V> {

  /** Constructor for use by subclasses. */
  protected ForwardingNavigableMap() {}

  @Override
  protected abstract NavigableMap<K, V> delegate();

  @Override
  public @Nullable Entry<K, V> lowerEntry(@ParametricNullness K key) {

@GwtIncompatible
public abstract class ForwardingNavigableMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingSortedMap<K, V> implements NavigableMap<K, V> {

  /** Constructor for use by subclasses. */
  protected ForwardingNavigableMap() {}

  @Override
  protected abstract NavigableMap<K, V> delegate();

  @Override
  public @Nullable Entry<K, V> lowerEntry(@ParametricNullness K key) {

import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;
import org.jspecify.annotations.Nullable;
import sun.security.jca.ProviderList;
import sun.security.jca.Providers;

/**
 * Tests for the MacHashFunction.
 *
 * @author Kurt Alfred Kluever
 */
@NullUnmarked

    return forwardMultiset();
  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    return forwardMultiset().lastEntry();
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    return forwardMultiset().firstEntry();
  }

  abstract Iterator<Entry<E>> entryIterator();

  @Nullable private transient Set<Entry<E>> entrySet;

  @Override

   *
   * <p>The serialized output consists of the number of entries, first key, first value, second key,
   * second value, and so on.
   */
  static <K extends @Nullable Object, V extends @Nullable Object> void writeMap(
      Map<K, V> map, ObjectOutputStream stream) throws IOException {
    stream.writeInt(map.size());
    for (Map.Entry<K, V> entry : map.entrySet()) {

   */
  public static <T extends @Nullable Object> Predicate<T> notNull() {
    return ObjectPredicate.NOT_NULL.withNarrowedType();
  }

  /**
   * Returns a predicate that evaluates to {@code true} if the given predicate evaluates to {@code
   * false}.
   *
   * <p><b>Discouraged:</b> Prefer using {@code predicate.negate()}.
   */
  public static <T extends @Nullable Object> Predicate<T> not(Predicate<T> predicate) {

    return forwardMultiset();
  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    return forwardMultiset().lastEntry();
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    return forwardMultiset().firstEntry();
  }

  abstract Iterator<Entry<E>> entryIterator();

  @LazyInit private transient @Nullable Set<Entry<E>> entrySet;

  @Override