public KafkaFuture<Collection<ClientMetricsResourceListing>> all() {
        final KafkaFutureImpl<Collection<ClientMetricsResourceListing>> result = new KafkaFutureImpl<>();
        future.whenComplete((listings, throwable) -> {
            if (throwable != null) {
                result.completeExceptionally(throwable);
            } else {
                result.complete(listings);
            }
        });
        return result;
    }
Returns a future that yields either an exception, or the full set of client metrics
listings.

In the event of a failure, the future yields nothing but the first exception which
occurred.
clients/src/main/java/org/apache/kafka/clients/admin/ListClientMetricsResourcesResult.java