Avp Using Dbtext

I´m trying to use DBTEXT DB with avpops but I didn´t see anything being stored.

I used the following:

...
modparam("avpops", "avp_url","dbtext:///etc/openser/dbtext")
modparam("avpops", "avp_table","usr_preferences")

...
if (is_method("REGISTER"))
{
if (registered("location")) {
xlog("L_DGB"," \nSubscriber: $ru unregistred\n");
}else{
if (!save("location"))
sl_reply_error();
xlog("L_DGB"," \nSubscriber: $ru REGISTRED\n");
}
avp_db_store("$ru", "$avp(s:22)");
avp_print();
exit;
}

I see in log:
DBG:avpops:ops_dbstore_avps: 0 avps were stored

I appreciate any help on this,
Thanks in advance.