SQL & PL/SQL

We are using SQLDeveloper and almost every stored procedure I compile I get this warning. If I had it my way, I would not use SQLDeveloper but due to budget restrictions this is all I have.

Here is the piece of code I am getting this warning on.

select count(*)
into dup_cnt
FROM trans
WHERE trans.ID_SSN = SSN_NUM
AND trans_cd = 'DU'
and trans_date between '01-NOV-'||to_char(to_number(to_char(sysdate,'YYYY')-1)) and trunc(sysdate);

Thank you for taking time to look at this.
Sandeep.