ORA-01476: divisor is equal to zero

create table tq84_div (
   n1  number,
   n2  number
);

insert into tq84_div values (42,    7);
insert into tq84_div values (99, null);
insert into tq84_div values ( 1,    0);
insert into tq84_div values (21,    3);

select
   n1,
   n2,
   n1/n2            division_by_zero_error
from
   tq84_div;

select
   n1,
   n2,
   n1/nullif(n2, 0) no_divizion_by_zero_error
from
   tq84_div;