this.delegate = checkNotNull(delegate);
  }

  /**
   * Wraps a {@code Callable} for submission to the underlying executor. This method is also applied
   * to any {@code Runnable} passed to the default implementation of {@link #wrapTask(Runnable)}.
   */
  protected abstract <T extends @Nullable Object> Callable<T> wrapTask(Callable<T> callable);

  /**

  abstract <R> @Nullable R dummyReturnValue(TypeToken<R> returnType);

  private final class DummyHandler extends AbstractInvocationHandler implements Serializable {
    private final TypeToken<?> interfaceType;

    DummyHandler(TypeToken<?> interfaceType) {
      this.interfaceType = interfaceType;
    }

    @Override
    protected @Nullable Object handleInvocation(

  @Override
  public Comparator<? super E> comparator() {
    return comparator;
  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();

  public abstract UnmodifiableIterator<E> iterator();

  @Override
  public boolean contains(@Nullable Object object) {
    return object != null && super.contains(object);
  }

  @Override
  public final boolean add(E e) {
    throw new UnsupportedOperationException();
  }

  @Override
  public final boolean remove(@Nullable Object object) {
    throw new UnsupportedOperationException();
  }

  @Override

   * equal to any other equality groups added to this tester.
   *
   * <p>The {@code @Nullable} annotations on the {@code equalityGroup} parameter imply that the
   * objects, and the array itself, can be null. That is for programmer convenience, when the
   * objects come from factory methods that are themselves {@code @Nullable}. In reality neither the
   * array nor its contents can be null, but it is not useful to force the use of {@code

import static java.util.Collections.singletonMap;

import org.jspecify.annotations.Nullable;

/**
 * GWT emulation of {@link SingletonImmutableBiMap}.
 *
 * @author Hayward Chan
 */
final class SingletonImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {
  private final K singleKey;
  private final V singleValue;

  @Nullable transient SingletonImmutableBiMap<V, K> inverse;

  SingletonImmutableBiMap(K key, V value) {

  private static final class AlwaysEqual extends Ordering<@Nullable Object>
      implements Serializable {
    private static final AlwaysEqual INSTANCE = new AlwaysEqual();

    @Override
    @SuppressWarnings("UnusedVariable") // intentionally weird Comparator
    public int compare(@Nullable Object o1, @Nullable Object o2) {
      return 0;
    }

    @Override

        // Default constructor
    }

    /**
     * Creates an OptionalEntity from a nullable entity.
     *
     * @param <T> the type of the entity
     * @param entity the entity (can be null)
     * @return the OptionalEntity
     */
    public static <T> OptionalEntity<T> ofNullable(final T entity) {
        return OptionalEntity.ofNullable(entity, () -> {});
    }

import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/** Replacements for JUnit's {@code assertThrows} that work under GWT/J2CL. */
@GwtCompatible
@NullMarked
final class ReflectionFreeAssertThrows {
  interface ThrowingRunnable {
    void run() throws Throwable;
  }

  interface ThrowingSupplier {
    @Nullable Object get() throws Throwable;
  }

  @CanIgnoreReturnValue

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.stream.Collector;
import jsinterop.annotations.JsMethod;
import org.jspecify.annotations.Nullable;

/**
 * GWT emulated version of {@link com.google.common.collect.ImmutableSet}. For the unsorted sets,
 * they are thin wrapper around {@link java.util.Collections#emptySet()}, {@link