guardTransition example

if (!$marking->has($place)) {
                return new TransitionBlockerList([
                    TransitionBlocker::createBlockedByMarking($marking),
                ]);
            }
        }

        if (null === $this->dispatcher) {
            return new TransitionBlockerList();
        }

        $event = $this->guardTransition($subject, $marking, $transition);

        if ($event->isBlocked()) {
            return $event->getTransitionBlockerList();
        }

        return new TransitionBlockerList();
    }

    private function guardTransition(object $subject, Marking $marking, Transition $transition): ?GuardEvent
    {
        if (null === $this->dispatcher) {