@Override
    public CompletableFuture<List<T>> collect(EventExecutor executor, SubscriptionOption... options) {
        whenComplete().complete(null);
        return UnmodifiableFuture.completedFuture(ImmutableList.of());
    }
A {@link FixedStreamMessage} that publishes no objects, just a close event.
core/src/main/java/com/linecorp/armeria/internal/common/stream/EmptyFixedStreamMessage.java