PL/SQL related question

I'm currently doing a project in oracle PL/SQL, I am somewhat new to this language, and I have a question:
If I try to do something like this:

select id
into id_aux
from clients
where name=name_input;

and if there are no clients with the name=name_input, what happens to id_aux?
Does it remain the same, is it set to NULL, is there any exception I can use?
I am asking this because I am thinking of using "id_aux" as a control variable.