Just use the nvl (null value) function eg
nvl(fin1,0)
This would treat any null in the field fin1 as 0
This could be used like this:-
select nvl(fin1,0), nvl(fin2,0), nvl(fin1,0) + nvl(fin2,0) as total from mytable;
to give:-
fin1 fin2 total
0 1200 1200
etc.