Why just use a simple SQL query for that, like this one:
select xxx from table_names where created_date is null or (created_date >= to_date("02/09/2010", "dd/mm/yyyy") and created_date <= to_date("03/09/2010", "dd/mm/yyyy"));
Edit
You can define a query like the one defined by ammoQ, i.e. something like that:
select xxx from table_names where created_date is null or created_date >= start_date and created_date <= nvl(end_date, to_date("31/12/9999", "dd/mm/yyyy"));
However, as you are using PL/SQL, you can check the nullability of end_date
parameter:
IF end_date IS NULL THEN
select xxx from table_names where created_date is null or created_date >= start_date;
ELSIF
select xxx from table_names where created_date is null or created_date >= start_date and created_date <= end_date;
END IF;
Note that you can remove the created_date is null
condition if created_date
is not a nullable column...