SQL & PL/SQL :: Function Raise No Error When Call In Select

why function does no raise error no_data found when call in select statement.

1) create one function.

CREATE OR REPLACE function fn_sal(v_id NUMBER) RETURN NUMBER
IS
v_sal NUMBER;
BEGIN
SELECT sal INTO v_sal FROM emp where empno=0;
RETURN v_sal;
END;

2) call it in select statement.

SELECT fn_sal(e.sal),e.* FROM emp e

select satement cause no error , it displayes all the records but null for the function cloumn.

why it not gives no_data_found error.