public Map<String, KafkaFuture<Void>> fencedProducers() {
        return futures.entrySet().stream().collect(Collectors.toMap(
            e -> e.getKey().idValue,
            e -> e.getValue().thenApply(p -> null)
        ));
    }
Return a map from transactional ID to futures which can be used to check the status of
individual fencings.
clients/src/main/java/org/apache/kafka/clients/admin/FenceProducersResult.java