@Override
    public CompletableFuture<AggregatedMultipart> aggregateWithPooledObjects(ByteBufAllocator alloc) {
        requireNonNull(alloc, "alloc");
        return aggregateWithPooledObjects(defaultSubscriberExecutor(), alloc);
    }
Returns a random boundary used for encoding multipart messages.
core/src/main/java/com/linecorp/armeria/common/multipart/DefaultMultipart.java