import java.util.concurrent.Callable;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterator.OfPrimitive;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;

import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.EnumMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Spliterator;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.stream.Collector;

import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Currency;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.NavigableMap;

    assertNull(Optional.toJavaUtil(null));
    assertEquals(java.util.Optional.empty(), Optional.toJavaUtil(Optional.absent()));
    assertEquals(java.util.Optional.of("abc"), Optional.toJavaUtil(Optional.of("abc")));
  }

  public void testToJavaUtil_instance() {
    assertEquals(java.util.Optional.empty(), Optional.absent().toJavaUtil());
    assertEquals(java.util.Optional.of("abc"), Optional.of("abc").toJavaUtil());
  }

import com.google.common.util.concurrent.ExecutionError;
import com.google.common.util.concurrent.UncheckedExecutionException;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Spliterator;
import java.util.function.Consumer;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Provides static methods for working with {@code Collection} instances.
 *

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import junit.framework.Test;
import junit.framework.TestCase;

import java.security.SecurityPermission;
import java.util.Arrays;
import java.util.Date;
import java.util.NoSuchElementException;
import java.util.PropertyPermission;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;

import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.stream.Collector;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;