return (Optional<T>) INSTANCE;
  }

  private Absent() {}

  @Override
  public boolean isPresent() {
    return false;
  }

  @Override
  public T get() {
    throw new IllegalStateException("Optional.get() cannot be called on an absent value");
  }

  @Override
  public T or(T defaultValue) {
    return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
  }

  }

  /**
   * Wrapper for {@link Map#get(Object)} that forces the caller to pass in a key of the same type as
   * the map. Besides being slightly shorter than code that uses {@link #getMap()}, it also ensures
   * that callers don't pass an {@link Entry} by mistake.
   */
  protected V get(K key) {
    return getMap().get(key);
  }

  protected final K k0() {
    return e0().getKey();
  }

    assertTrue(task.isDone());
    assertTrue(task.isCancelled());
    assertTrue(task.wasInterrupted());
    try {
      task.get();
      fail();
    } catch (CancellationException expected) {
    }
    exitLatch.await();
    assertTrue(interruptedExceptionThrown.get());
  }

  @J2ktIncompatible
  @GwtIncompatible // blocking wait
  public void testRunIdempotency() throws Exception {

    assertEqualIgnoringOrder(values, multimap().get(key));

    if (!values.isEmpty()) {
      assertEqualIgnoringOrder(values, multimap().asMap().get(key));
      assertFalse(multimap().isEmpty());
    } else {
      assertNull(multimap().asMap().get(key));
    }

    assertEquals(values.size(), multimap().get(key).size());

    assertEquals(values.size() > 0, multimap().containsKey(key));

        for (int i = 1; i < keys.size(); i++) {
          if (keys.get(i) < keys.get(minIndex)) {
            minIndex = i;
          }
        }
        Optional<BinaryNode> leftChild = createTreap(keys.subList(0, minIndex));
        Optional<BinaryNode> rightChild = createTreap(keys.subList(minIndex + 1, keys.size()));
        return Optional.of(new BinaryNode(keys.get(minIndex), leftChild, rightChild));
      }
    };

   * The version of this test supplied by {@link MapInterfaceTest} fails for this particular Map
   * implementation, because {@code map.get()} returns a view collection that changes in the course
   * of a call to {@code remove()}. Thus, the expectation doesn't hold that {@code map.remove(x)}
   * returns the same value which {@code map.get(x)} did immediately beforehand.
   */
  @Override
  public void testRemove() {

  @Override
  protected abstract LoadingCache<K, V> delegate();

  @CanIgnoreReturnValue // TODO(b/27479612): consider removing this
  @Override
  public V get(K key) throws ExecutionException {
    return delegate().get(key);
  }

  @CanIgnoreReturnValue // TODO(b/27479612): consider removing this
  @Override
  public V getUnchecked(K key) {
    return delegate().getUnchecked(key);
  }

    try {
      future.get();
      Assert.fail("This call was supposed to throw an ExecutionException");
    } catch (ExecutionException expected) {
      Assert.assertSame(expectedCause, expected.getCause());
    }
  }

  public void assertTimeout() throws Exception {
    // Verify that the listener does not get called in a reasonable amount of
    // time.

              .replace("$OTHER", itemReporter.reportItem(other)));
    }
  }

  private Item<T> getItem(int groupNumber, int itemNumber) {
    return new Item<>(groups.get(groupNumber).get(itemNumber), groupNumber, itemNumber);
  }

  static final class Item<T> {
    final T value;
    final int groupNumber;
    final int itemNumber;

      fail("Expected UnsupportedOperationException");
    } catch (UnsupportedOperationException expected) {
    }
    assertEquals((Character) 'a', table.get("foo", 1));
    assertEquals((Character) 'b', table.get("bar", 1));
    assertEquals((Character) 'c', table.get("foo", 3));
    assertSize(3);
  }

  @Override
  public void testPutNull() {}

  @Override
  public void testPutNullReplace() {}

  @Override