*       directExecutor}, the listener can execute in any of three possible threads:
   *       <ol>
   *         <li>When a thread attaches a listener to a {@code ListenableFuture} that's already
   *             complete, the listener runs immediately in that thread.
   *         <li>When a thread attaches a listener to a {@code ListenableFuture} that's
   *             incomplete and the {@code ListenableFuture} later completes normally, the

    }

    @Override
    public Iterator<Entry<K, V>> iterator() {
      return unmodifiableEntryIterator(entries.iterator());
    }

    // See java.util.Collections.UnmodifiableEntrySet for details on attacks.

    @Override
    public @Nullable Object[] toArray() {
      /*
       * standardToArray returns `@Nullable Object[]` rather than `Object[]` but because it can