* Contrast the method above to:
 *
 * <ul>
 *   <li>methods whose return type is a type variable but which can never return {@code null},
 *       typically because the type forbids nullable type arguments: For example, {@code
 *       ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,

  private transient volatile @Nullable CacheEntry<K, V> cacheEntry2;

  MapRetrievalCache(Map<K, V> backingMap) {
    super(backingMap);
  }

  @SuppressWarnings("unchecked") // Safe because we only cast if key is found in map.
  @Override
  @Nullable V get(Object key) {
    checkNotNull(key);
    V value = getIfCached(key);
    if (value != null) {
      return value;
    }

      return;
    }

    /*
     * Any of the setException() calls below can fail if the output Future is cancelled between now
     * and then. This means that we're silently swallowing an exception -- maybe even an Error. But
     * this is no worse than what FutureTask does in that situation. Additionally, because the

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      closeLater(ErrorCode.CANCEL)
      connection.sendDegradedPingLater()
    }

    override fun newTimeoutException(cause: IOException?): IOException =
      SocketTimeoutException("timeout").apply {
        if (cause != null) {
          initCause(cause)
        }
      }

    @Throws(IOException::class)
    fun exitAndThrowIfTimedOut() {
      if (exit()) throw newTimeoutException(null)

      return;
    }

    /*
     * Any of the setException() calls below can fail if the output Future is cancelled between now
     * and then. This means that we're silently swallowing an exception -- maybe even an Error. But
     * this is no worse than what FutureTask does in that situation. Additionally, because the

   * the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
   * documentation.
   */
  public void add(Runnable runnable, Executor executor) {
    // Fail fast on a null. We throw NPE here because the contract of Executor states that it throws
    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");

   * have the provided key, an empty collection is returned.
   *
   * <p>Changes to the returned collection will update the underlying multimap, and vice versa.
   *
   * <p>Because a {@code SortedSetMultimap} has unique sorted values for a given key, this method
   * returns a {@link SortedSet}, instead of the {@link java.util.Collection} specified in the
   * {@link Multimap} interface.
   */
  @Override

      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEY_QUERIES)
  public void testReplace_absentNullKeyUnsupported() {
    try {
      getMap().replace(null, v3());
    } catch (NullPointerException tolerated) {
      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEY_QUERIES)
  public void testReplace_absentNullKeyUnsupported() {
    try {
      getMap().replace(null, v3());
    } catch (NullPointerException tolerated) {
      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }