create table null_cols (col_1 number, col_2 number, col_3 number);

insert into null_cols values (null,null,null);
insert into null_cols values (null,null,1);
insert into null_cols values (1,1,null);
insert into null_cols values (1,1,1);

select nvl2(col_1,0,1) + nvl2(col_2,0,1) + nvl2(col_3,0,1) null_columns
      ,col_1
      ,col_2
      ,col_3
from   null_cols;

create table succeeded.
1 rows inserted
1 rows inserted
1 rows inserted
1 rows inserted
NULL_COLUMNS           COL_1                  COL_2                  COL_3                  
---------------------- ---------------------- ---------------------- ---------------------- 
3                                                                                           
2                                                                    1                      
1                      1                      1                                             
0                      1                      1                      1                      

4 rows selected