[Dovecot] I can't setup namespace per user (with settings keept in sql db)

[Marcin Mirosław]

Hello!
I'm trying to setup additional namespace. I'd like to have this setting
per user and keep it in postgresql.
Global namespace is defined in this way:
namespace {
  inbox = yes
  location =
  prefix =
  separator = .
}
(mail_location is getting from db)
I don't know how should looks like database field:(
Now i have such configuration:
user_query = select .... dovecot_location AS location, dovecot_namespace
AS namespace FROM ...

In db i have this:
# select dovecot_location, dovecot_namespace from exim_users where
dovecot_namespace is not null;
     dovecot_location      | dovecot_namespace
---------------------------+-------------------
 location="mdbox:~/.mdbox" | prefix="testn"
(1 row)

but this isn't good configuration. I've got in log:

debug: sql(marcin at mejor.pl,62.121.127.119): SELECT
'/dane/domeny/mejor.pl/mail/marcin/' as home, dovecot_typ_skrzynki
||':'|| '/dane/domeny/mejor.pl/mail/marcin/' ||'
.'|| dovecot_typ_skrzynki as mail_location, '*:bytes='||quota_mb||'M' as
quota_rule , dovecot_location AS location, dovecot_namespace AS
namespace FROM exim_users WHE
RE login = lower('marcin') AND domena = lower('mejor.pl')
Debug: master out:
USER#0112138832897#011marcin at mejor.pl#011home=/dane/domeny/mejor.pl/mail/marcin/#011mail_location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildi
r#011quota_rule=*:bytes=0M#011location=location="mdbox:~/.mdbox"#011namespace=prefix="testn"
Login: user=<marcin at mejor.pl>, method=CRAM-MD5, rip=62.121.127.119,
lip=193.238.12.139, mpid=17929, TLS
Debug: Loading modules from directory: /usr/lib/dovecot
Debug: Module loaded: /usr/lib/dovecot/lib10_quota_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib11_imap_quota_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib15_notify_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_autocreate_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_fts_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_mail_log_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_zlib_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib21_fts_squat_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib30_imap_zlib_plugin.so
Debug: Added userdb setting:
mail_location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: Added userdb setting: plugin/quota_rule=*:bytes=0M
Debug: Added userdb setting: plugin/location=location="mdbox:~/.mdbox"
Debug: Added userdb setting: namespace=prefix="testn"
Debug: Effective uid=8, gid=12, home=/dane/domeny/mejor.pl/mail/marcin/
Debug: Quota root: name=User quota backend=dict args=:proxy::quota
Debug: Quota rule: root=User quota mailbox=* bytes=0 messages=0
Debug: dict quota: user=marcin at mejor.pl, uri=proxy::quota, noenforcing=0
Debug: Namespace : type=private, prefix=, sep=., inbox=yes, hidden=no,
list=yes, subscriptions=yes
location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: maildir++: root=/dane/domeny/mejor.pl/mail/marcin/.maildir,
index=, control=, inbox=/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: Namespace : type=private, prefix=, sep=, inbox=no, hidden=no,
list=yes, subscriptions=yes
location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: maildir++: root=/dane/domeny/mejor.pl/mail/marcin/.maildir,
index=, control=, inbox=
Error: user marcin at mejor.pl: Initialization failed: namespace
configuration error: Duplicate namespace prefix: ""
Error: Invalid user settings. Refer to server log for more information.

I've got stuck, i don't have idea how configuration should looks:(
Thanks for any help!
dovceot-2.0.13