SQL> ed
Wrote file afiedt.buf

  1  with t(a,b,c) as(
  2  select 1,2,3 from dual union all
  3  select null,4,5 from dual union all
  4  select 6,null,7 from dual union all
  5  select 8,9,null from dual
  6  )
  7* select a,b,a+b c from t
SQL> /

         A          B          C
---------- ---------- ----------
         1          2          3
null                4 null
         6 null       null
         8          9         17

SQL>

  1  with t as (select 2 a, -2 b  from dual)
  2* select a,b, (power(a,2)+2*a*b+b*b)/(a+b) as c from t
SQL> /
select a,b, (power(a,2)+2*a*b+b*b)/(a+b) as c from t
                                  *
ERROR at line 2:
ORA-01476: divisor is equal to zero