// This reference is only used by GWT compiler to infer the keys and values
  // of the map that needs to be serialized.
  private @Nullable Comparator<? super K> unusedComparatorForSerialization;
  private @Nullable K unusedKeyForSerialization;
  private @Nullable V unusedValueForSerialization;

  private final transient SortedMap<K, V> sortedDelegate;

  }

  public void testCopyOf_nullArray() {
    assertThrows(NullPointerException.class, () -> copyOf((String[]) null));
  }

  public void testCopyOf_arrayContainingOnlyNull() {
    @Nullable String[] array = new @Nullable String[] {null};
    assertThrows(NullPointerException.class, () -> copyOf((String[]) array));
  }

  public void testCopyOf_collection_empty() {

import com.google.common.annotations.GwtCompatible;
import java.util.Queue;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Creates queues, containing sample elements, to be tested.
 *
 * @author Jared Levy
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TestQueueGenerator<E extends @Nullable Object> extends TestCollectionGenerator<E> {
  @Override
  Queue<E> create(Object... elements);

import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Creates sets, containing sample elements, to be tested.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TestListGenerator<E extends @Nullable Object> extends TestCollectionGenerator<E> {
  @Override
  List<E> create(Object... elements);

import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Iterator;
import java.util.Queue;
import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link Synchronized#queue} and {@link Queues#synchronizedQueue}.
 *
 * @author Kurt Alfred Kluever
 */
public class SynchronizedQueueTest extends TestCase {

            ? super AggregateFutureState<?>, ? super @Nullable Set<Throwable>>
        seenExceptionsUpdater;

    final AtomicIntegerFieldUpdater<? super AggregateFutureState<?>> remainingCountUpdater;

    SafeAtomicHelper(
        AtomicReferenceFieldUpdater<
                ? super AggregateFutureState<?>, ? super @Nullable Set<Throwable>>
            seenExceptionsUpdater,

import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicBoolean;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Utilities necessary for working with libraries that supply plain {@link Future} instances. Note
 * that, whenever possible, it is strongly preferred to modify those libraries to return {@code

  /**
   * To avoid infinite recursion, test suites with these marker features won't have derived suites
   * created for them.
   */
  enum NoRecurse implements Feature<@Nullable Void> {
    SUBMAP,
    DESCENDING;

    @Override
    public Set<Feature<? super @Nullable Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  /**
   * Creates a suite whose map has some elements filtered out of view.
   *

import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Iterator;
import java.util.Queue;
import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link Synchronized#queue} and {@link Queues#synchronizedQueue}.
 *
 * @author Kurt Alfred Kluever
 */
public class SynchronizedQueueTest extends TestCase {

import java.lang.invoke.MethodType;
import java.lang.reflect.UndeclaredThrowableException;
import java.nio.ByteBuffer;
import java.util.zip.Checksum;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * {@link HashFunction} adapter for {@link Checksum} instances.
 *
 * @author Colin Decker
 */
@Immutable
@ElementTypesAreNonnullByDefault