@SuppressWarnings("unchecked")
    @Override
    public StreamMessageDuplicator<T> toDuplicator(EventExecutor executor) {
        return (StreamMessageDuplicator<T>) delegate().toDuplicator(executor);
    }
Returns the {@link StreamMessage} being decorated.
core/src/main/java/com/linecorp/armeria/common/stream/StreamMessageWrapper.java