Connected to Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 
CREATE OR REPLACE FUNCTION test_f  RETURN NUMBER IS
 i NUMBER;
BEGIN
   select 1 into i from dual where 0 = 1;
  RETURN 0;
END;
/
SQL> select nvl(test_f,-1) from dual;

NVL(TEST_F,-1)
--------------
            -1

declare i number; begin i:=test_f; end;
/
ORA-01403: no data found
ORA-06512: at "TORG.TEST_F", line 4
ORA-06512: at line 1