private static final @Nullable Object jla = getJla();

  /**
   * The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
   * find it when available. When this is null, use the slow way.
   */
  @J2ktIncompatible @GwtIncompatible // java.lang.reflect
  private static final @Nullable Method getStackTraceElementMethod =

      List<@Nullable String> listWithNulls = asList("a", null, "b");
      assertThrows(NullPointerException.class, () -> builder.addAll((List<String>) listWithNulls));
    }

    {
      ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
      Multiset<@Nullable String> multisetWithNull =
          LinkedHashMultiset.create(Arrays.<@Nullable String>asList("a", null, "b"));

      return standardSubMultiset(lowerBound, lowerBoundType, upperBound, upperBoundType);
    }

    @Override
    public int count(@Nullable Object element) {
      return standardCount(element);
    }

    @Override
    public boolean equals(@Nullable Object object) {
      return standardEquals(object);
    }

    @Override
    public int hashCode() {
      return standardHashCode();
    }

 * methods that they depend on are thread-safe.
 *
 * @author Mike Bostock
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingMapEntry<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingObject implements Map.Entry<K, V> {
  // TODO(lowasser): identify places where thread safety is actually lost

  /** Constructor for use by subclasses. */

    @Override
    public boolean equals(@Nullable Object other) {
      return (other instanceof ClassWhichIsAlwaysEqualButHasDifferentHashcodes);
    }
  }

  private static class ObjectWhichIsEqualButChangesClass implements Serializable {
    private static final long serialVersionUID = 1L;

    @Override
    public boolean equals(@Nullable Object other) {

  }

  @Override
  public @Nullable V value(N node) {
    return adjacentNodeValues.get(node);
  }

  @Override
  public void removePredecessor(N node) {
    @SuppressWarnings("unused")
    V unused = removeSuccessor(node);
  }

  @Override
  public @Nullable V removeSuccessor(N node) {
    return adjacentNodeValues.remove(node);
  }

  @Override

import com.google.common.annotations.GwtCompatible;
import java.util.SortedMap;
import org.jspecify.annotations.Nullable;

/**
 * An object representing the differences between two sorted maps.
 *
 * @author Louis Wasserman
 * @since 8.0
 */
@GwtCompatible
public interface SortedMapDifference<K extends @Nullable Object, V extends @Nullable Object>
    extends MapDifference<K, V> {

  @Override
  SortedMap<K, V> entriesOnlyOnLeft();

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

/**
 * A generator for {@code ListMultimap} implementations based on test data.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@NullMarked
public interface TestListMultimapGenerator<K extends @Nullable Object, V extends @Nullable Object>

    public CustomScheduler() {}

    /** A callable class that can reschedule itself using a {@link CustomScheduler}. */
    private final class ReschedulableCallable implements Callable<@Nullable Void> {

      /** The underlying task. */
      private final Runnable wrappedRunnable;

      /** The executor on which this Callable will be scheduled. */
      private final ScheduledExecutorService executor;

      assertTrue(Thread.holdsLock(mutex));
      return delegate.containsRow(rowKey);
    }

    @Override
    public @Nullable V get(Object rowKey, Object columnKey) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.get(rowKey, columnKey);
    }

    @Override
    public @Nullable V put(R rowKey, C columnKey, V value) {
      assertTrue(Thread.holdsLock(mutex));