SQL Developer

Hi all,

I have this query that returns the production of the last 12 months.
This is the query:

select
    null
  , sum(f.comision)         value
  , trunc(f.efectiva, 'MM') label
from
    risk_facturas f
where
    f.efectiva >= add_months(trunc(sysdate), -13) and f.efectiva < trunc(sysdate) + 1
and f.organizacion_id = :APP_GET_ORGANIZACION_ID
group by
    trunc(f.efectiva, 'MM')

How can I get a line for every month no matter if it has any production or is just 0? Can this be done?
Thanks for the help!
Javier