*/
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

 */
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

  }

  // common.base
  @Empty
  <T> com.google.common.base.Optional<T> generateGoogleOptional() {
    return com.google.common.base.Optional.absent();
  }

  @Generates
  <T> com.google.common.base.Optional<T> generateGoogleOptional(T value) {
    return com.google.common.base.Optional.of(value);
  }

  @Generates
  Joiner generateJoiner() {

    return pickInstance(Currency.getAvailableCurrencies(), Currency.getInstance(Locale.US));
  }

  @Empty
  <T> Optional<T> generateJavaOptional() {
    return Optional.empty();
  }

  @Generates
  <T> Optional<T> generateJavaOptional(T value) {
    return Optional.of(value);
  }

  @Generates
  OptionalInt generateOptionalInt() {
    return OptionalInt.of(generateInt());
  }

  public void testStream_googleOptional() {
    assertThat(stream(com.google.common.base.Optional.absent())).isEmpty();
    assertThat(stream(com.google.common.base.Optional.of("a"))).containsExactly("a");
  }

  public void testStream_javaOptional() {
    assertThat(stream(java.util.Optional.empty())).isEmpty();
    assertThat(stream(java.util.Optional.of("a"))).containsExactly("a");
  }

  public void testFindLast_refStream() {

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Comparator;

          .put(TimeUnit.class, TimeUnit.SECONDS)
          .put(Charset.class, Charsets.UTF_8)
          .put(Currency.class, Currency.getInstance(Locale.US))
          .put(Locale.class, Locale.US)
          .put(Optional.class, Optional.empty())
          .put(OptionalInt.class, OptionalInt.empty())
          .put(OptionalLong.class, OptionalLong.empty())
          .put(OptionalDouble.class, OptionalDouble.empty())

    public void refresh(K key) {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * LinkedHashMap that enforces it's maximum size and logs events in a StatsCounter object and an
   * optional RemovalListener.
   *
   * @param <K> the base key type
   * @param <V> the base value type
   */
  private class CapacityEnforcingLinkedHashMap<K, V> extends LinkedHashMap<K, Timestamped<V>> {

          .put(CharMatcher.class, CharMatcher.none())
          .put(Joiner.class, Joiner.on(','))
          .put(Splitter.class, Splitter.on(','))
          .put(com.google.common.base.Optional.class, com.google.common.base.Optional.absent())
          .put(Predicate.class, Predicates.alwaysTrue())
          .put(Equivalence.class, Equivalence.equals())
          .put(Ticker.class, Ticker.systemTicker())

 *
 * <p>By default, {@code BaseEncoding}'s behavior is relatively strict and in accordance with RFC
 * 4648. Decoding rejects characters in the wrong case, though padding is optional. To modify
 * encoding and decoding behavior, use configuration methods to obtain a new encoding with modified
 * behavior:
 *
 * <pre>{@code
 * BaseEncoding.base16().lowerCase().decode("deadbeef");
 * }</pre>
 *