You asked this similar question yesterday.
Could you please tell us if the answer provided was not useful, or your question was misunderstood ?
It would be also useful to know why you can’t use the IF – THEN -ENDIF approach.
Examples always help. Could you provide some example, or tell us what exactly you want your procedure to do when the address is null (please be as specific as possible)?
I would create a before insert trigger (code below assumes table name is ADDRESS)
create or replace trigger trg_address_bi
referencing NEW as new OLD as OLD
For each row
if :new.address3 is null then
:new.address3 := '-';