code: public <T> Completes<Optional<T>> maybeActorOf(final Class<T> protocol, final Address address) {
      return directoryScanner.maybeActorOf(protocol, address).andThen(proxy -> proxy);
    }
docs: Answer the {@code protocol} reference of the actor with {@code address} as a non-empty
  {@code Completes<Optional<T>>} eventual outcome, or an empty {@code Completes<Optional<T>>}
  if not found.
  @param protocol the {@code Class<T>} of the protocol that the actor must support
  @param address the {@code Address} of the actor to find
  @param <T> the protocol type
  @return {@code Completes<Optional<T>>}