SQL>
SQL> -- declare not null variable
SQL>
SQL> declare
2 l_number number not null := 1;
3 l_another_number number;
4 begin
5 l_number := 2;
6 l_number := l_another_number;
7 end;
8 /
declare
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 6
SQL>