Too_many_rows exception behavior in 12c

Hi All,

We are migrating from oracle 11g to 12c. The table#Prt_PrGrp_Part_Group_Info has 3 records for the below condition. The select statement assigns 'Y' into EXIST_FLAG_TMP in 11g and the same is not getting assigned in 12c(12.2) when it comes through application. The same piece of code is working in 12.1.

DECLARE

EXIST_FLAG_TMP VARCHAR2(1);

BEGIN

EXIST_FLAG_TMP := 'N';

BEGIN

SELECT  'Y' INTO EXIST_FLAG_TMP

        FROM  Prt_PrGrp_Part_Group_Info

        WHERE PrGrp_Crt_OUInstance  = 2

        AND      PrGrp_Status     = 'A';

        EXCEPTION WHEN others THEN NULL;

END;

END;

/

Is there any behavior changes when exact fetch returns more than one row in both versions.