[FIX] UnboundLocalError
[IMP] improve fix by using browse_null instead of None for default partner value
[MRG] resolved merge conflict
[FIX] currency for poland is PLN and not PLZ since 1995
[FIX] currency for poland is PLN and not PLZ since 1995
[FIX] lp:1204920, partner variable referenced before assignment
[FIX] lp:1204920, partner variable referenced before assignment
[FIX] lp:1281290, correct currency code on Poland
[FIX] lp:1281290, correct currency code on Poland