putAll(multimap);
  }

  @Override
  Map<K, Collection<V>> createAsMap() {
    return createMaybeNavigableAsMap();
  }

  /**
   * {@inheritDoc}
   *
   * <p>Creates an empty {@code TreeSet} for a collection of values for one key.
   *
   * @return a new {@code TreeSet} containing a collection of values for one key
   */
  @Override
  SortedSet<V> createCollection() {

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.truth.Truth.assertWithMessage;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyMap;
import static java.util.Collections.singleton;
import static java.util.Collections.singletonMap;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;

   *     to primitives
   * @throws NullPointerException if {@code collection} or any of its elements is null
   * @since 1.0 (parameter was {@code Collection<Double>} before 12.0)
   */
  public static double[] toArray(Collection<? extends Number> collection) {
    if (collection instanceof DoubleArrayAsList) {
      return ((DoubleArrayAsList) collection).toDoubleArray();
    }

import com.google.common.collect.testing.testers.SetHashCodeTester;
import com.google.common.testing.NullPointerTester;
import com.google.common.testing.SerializableTester;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;

   * half of that is more awkward to arrange...
   */
  private static <T> Iterable<T> iterable(Collection<T> collection) {
    // return collection::iterator;
    return new Iterable<T>() {
      @Override
      public Iterator<T> iterator() {
        return collection.iterator();
      }
    };
  }

  public void testEquals() {
    new EqualsTester()

    // the behaviour of the non-GWT implementation of newConcurrentHashSet().
    // On the other hand HashSet might be better for code size if apps aren't
    // already using Collections.newSetFromMap and ConcurrentHashMap.
    return Collections.newSetFromMap(new ConcurrentHashMap<E, Boolean>());
  }

  static <E extends @Nullable Object> Set<E> newLinkedHashSetWithExpectedSize(int expectedSize) {

import static java.util.Collections.emptyList;
import static java.util.Collections.singletonList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.Multimap;
import com.google.common.collect.testing.features.CollectionSize;
import com.google.common.collect.testing.features.MapFeature;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.junit.Ignore;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionSize;
import com.google.common.collect.testing.features.ListFeature;
import java.util.Collections;
import java.util.List;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@link List#replaceAll}. Can't be invoked directly; please see
 * {@link com.google.common.collect.testing.ListTestSuiteBuilder}.

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.util.Collections;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/** Implementation of an {@link Optional} containing a reference. */
@GwtCompatible
final class Present<T> extends Optional<T> {

import static com.google.common.graph.GraphConstants.INNER_LOAD_FACTOR;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterators;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**