final CountDownLatch exitLatch = new CountDownLatch(1);
    final TrustedListenableFutureTask<@Nullable Void> task =
        TrustedListenableFutureTask.create(
            new Callable<@Nullable Void>() {
              @Override
              public @Nullable Void call() throws Exception {
                enterLatch.countDown();
                new CountDownLatch(1).await(); // wait forever

public class ProtoLogger implements Logger {

    private final PrintWriter out;
    private final PrintWriter err;

    public ProtoLogger() {
        this(null, null);
    }

    public ProtoLogger(@Nullable OutputStream out, @Nullable OutputStream err) {
        this.out = new PrintWriter(toPsOrDef(out, System.out), true);
        this.err = new PrintWriter(toPsOrDef(err, System.err), true);
    }

 *
 * @author Kurt Alfred Kluever
 * @since 3.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingSortedSetMultimap<
        K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingSetMultimap<K, V> implements SortedSetMultimap<K, V> {

  /** Constructor for use by subclasses. */
  protected ForwardingSortedSetMultimap() {}

  @Override

import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Implementation of {@link Multimaps#filterKeys(SetMultimap, Predicate)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class FilteredKeySetMultimap<K extends @Nullable Object, V extends @Nullable Object>
    extends FilteredKeyMultimap<K, V> implements FilteredSetMultimap<K, V> {

    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector<@Nullable Object, ?, @Nullable Object> ONLY_ELEMENT =
      Collector.<@Nullable Object, ToOptionalState, @Nullable Object>of(
          ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,
          state -> {

package com.google.common.collect.testing;

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

/**
 * To be implemented by test generators of things that can contain elements. Such things include
 * both {@link Collection} and {@link Map}; since there isn't an established collective noun that

  // the same values as `elements` in hashed positions (plus nulls)
  @VisibleForTesting final transient @Nullable Object[] table;
  // 'and' with an int to get a valid table index.
  private final transient int mask;

  RegularImmutableSet(Object[] elements, int hashCode, @Nullable Object[] table, int mask) {
    this.elements = elements;
    this.hashCode = hashCode;
    this.table = table;
    this.mask = mask;

    /**
     * Check if the consumer POM feature is active.
     */
    public static boolean consumerPom(@Nullable Properties userProperties) {
        return doGet(userProperties, Constants.MAVEN_CONSUMER_POM, true);
    }

    /**
     * Check if the consumer POM feature is active.
     */
    public static boolean consumerPom(@Nullable Map<String, String> userProperties) {
        return doGet(userProperties, Constants.MAVEN_CONSUMER_POM, true);

import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A mutable type-to-instance map. See also {@link ImmutableTypeToInstanceMap}.
 *
 * @author Ben Yu
 * @since 13.0
 */
@ElementTypesAreNonnullByDefault
public final class MutableTypeToInstanceMap<B extends @Nullable Object>
    extends ForwardingMap<TypeToken<? extends @NonNull B>, B> implements TypeToInstanceMap<B> {

            @Nonnull Map<String, String> systemProperties,
            @Nonnull Path topDirectory,
            @Nullable Path rootDirectory,
            @Nullable InputStream in,
            @Nullable OutputStream out,
            @Nullable OutputStream err,
            @Nullable List<CoreExtension> coreExtensions) {
        this.parserRequest = requireNonNull(parserRequest);
        this.cwd = requireNonNull(cwd);