* operation throws an {@link UnsupportedOperationException}.
   *
   * <p>The returned entry is serializable.
   *
   * <p><b>Java 9 users:</b> consider using {@code java.util.Map.entry(key, value)} if the key and
   * value are non-null and the entry does not need to be serializable.
   *
   * @param key the key to be associated with the returned entry

  public final Object mutex = new Object[0]; // something Serializable

  protected <K, V> Map<K, V> create() {
    TestMap<K, V> inner = new TestMap<>(new HashMap<K, V>(), mutex);
    Map<K, V> outer = Synchronized.map(inner, mutex);
    return outer;
  }

  static class TestMap<K, V> extends ForwardingMap<K, V> implements Serializable {
    public final Object mutex;
    private final Map<K, V> delegate;

import static java.util.Objects.requireNonNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.Serializable;
import org.jspecify.annotations.Nullable;

/**
 * Utility class for converting between various ASCII case formats. Behavior is undefined for
 * non-ASCII input.
 *
 * @author Mike Bostock
 * @since 1.0
 */

import com.google.errorprone.annotations.concurrent.LazyInit;
import java.io.Serializable;
import org.jspecify.annotations.Nullable;

/** An ordering that uses the natural order of the values. */
@GwtCompatible
final class NaturalOrdering extends Ordering<Comparable<?>> implements Serializable {
  static final NaturalOrdering INSTANCE = new NaturalOrdering();

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.concurrent.atomic.AtomicLong;

/**
 * One or more variables that together maintain an initially zero {@code long} sum. When updates

import com.google.common.collect.Multiset.Entry;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.WeakOuter;
import java.io.Serializable;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link ImmutableMultiset} with zero or more elements.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 */
@GwtCompatible

import com.google.common.primitives.Primitives;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.Map.Entry;
import org.jspecify.annotations.Nullable;

/**
 * {@code entrySet()} implementation for {@link ImmutableMap}.
 *
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.Serializable;
import java.util.Map.Entry;
import org.jspecify.annotations.Nullable;

/**
 * {@code values()} implementation for {@link ImmutableMap}.
 *
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 */

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.Serializable;
import java.util.Iterator;

/** An ordering that uses the reverse of the natural order of the values. */
@GwtCompatible
final class ReverseNaturalOrdering extends Ordering<Comparable<?>> implements Serializable {
  static final ReverseNaturalOrdering INSTANCE = new ReverseNaturalOrdering();

  @Override