private void unsubscribeReceive(final Manager m) {
final var subscriptionId = receiveHandlers.entrySet()
.stream()
- .filter(e -> e.getValue().size() == 1 && e.getValue().get(0).first().equals(m))
+ .filter(e -> e.getValue().size() == 1 && e.getValue().getFirst().first().equals(m))
.map(Map.Entry::getKey)
.findFirst();
subscriptionId.ifPresent(this::unsubscribeReceive);