void *addReplyDeferredLen(client *c) {
    /* Note that we install the write event here even if the object is not
     * ready to be sent, since we are sure that before returning to the
     * event loop setDeferredAggregateLen() will be called. */
    if (prepareClientToWrite(c) != C_OK) return NULL;
    trimReplyUnusedTailSpace(c);
    listAddNodeTail(c->reply,NULL); /* NULL is our placeholder. */
    return listLast(c->reply);
}
void *addReplyDeferredLen(client *c) {
     
    if (prepareClientToWrite(c) != C_OK) return NULL;
    trimReplyUnusedTailSpace(c);
    listAddNodeTail(c->reply,NULL);  
    return listLast(c->reply);
}