void xtrimCommand(client *c) {
    robj *o;

    /* If the key does not exist, we are ok returning zero, that is, the
     * number of elements removed from the stream. */
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL
        || checkType(c,o,OBJ_STREAM)) return;
    stream *s = o->ptr;

    /* Argument parsing. */
    int trim_strategy = TRIM_STRATEGY_NONE;
    long long maxlen = 0;   /* 0 means no maximum length. */
    int approx_maxlen = 0;  /* If 1 only delete whole radix tree nodes, so
                               the maxium length is not applied verbatim. */

    /* Parse options. */
    int i = 2; /* Start of options. */
    for (; i < c->argc; i++) {
        int moreargs = (c->argc-1) - i; /* Number of additional arguments. */
        char *opt = c->argv[i]->ptr;
        if (!strcasecmp(opt,"maxlen") && moreargs) {
            trim_strategy = TRIM_STRATEGY_MAXLEN;
            char *next = c->argv[i+1]->ptr;
            /* Check for the form MAXLEN ~ <count>. */
            if (moreargs >= 2 && next[0] == '~' && next[1] == '\0') {
                approx_maxlen = 1;
                i++;
            }
            if (getLongLongFromObjectOrReply(c,c->argv[i+1],&maxlen,NULL)
                != C_OK) return;
            i++;
        } else {
            addReply(c,shared.syntaxerr);
            return;
        }
    }

    /* Perform the trimming. */
    int64_t deleted = 0;
    if (trim_strategy == TRIM_STRATEGY_MAXLEN) {
        deleted = streamTrimByLength(s,maxlen,approx_maxlen);
    } else {
        addReplyError(c,"XTRIM called without an option to trim the stream");
        return;
    }

    /* Propagate the write if needed. */
    if (deleted) {
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(NOTIFY_STREAM,"xtrim",c->argv[1],c->db->id);
        server.dirty += deleted;
    }
    addReplyLongLong(c,deleted);
}

The product does not correctly convert an object, resource, or structure from one type to a different type.