Kamailio version 4.4.2.
Consider this logic: $avp(s:testvar) = 'test'; avp_db_query("select value from test where id = 1","$avp(s:testvar)");
I don't know if this is intended behaviour. If row exists but "value" field is empty (not NULL), $avp(s:testvar) still seems to contain 'test' as value after the query. I think it should be ''.
This can be confusing.