code: protected <T> T parentAs(final Class<T> protocol) {
      if (lifeCycle.environment.isSecured()) {
        throw new IllegalStateException("A secured actor cannot provide its parent.");
      }
      final Actor parent = lifeCycle.environment.parent;
      return lifeCycle.environment.stage.actorProxyFor(protocol, parent, parent.lifeCycle.environment.mailbox);
    }
docs: Answers the parent of this {@code Actor} as the {@code T} protocol.
  @param protocol the {@code Class<T>} of the protocol
  @param <T> the protocol type
  @return T