PLSQL Collection Check Existence

SET serveroutput ONSET verify OFFDECLAREtype a_typeIS  TABLE OF VARCHAR2(10) INDEX BY binary_integer;  a a_type;BEGIN  a(5)  := 'five';  a(-3) := 'minus 3';  a(0)  := 'zero';  a(7)  := 'seven';  a(9)  := 'nine';  DBMS_OUTPUT.PUT_LINE(A(2));EXCEPTIONWHEN no_data_found THEN  DBMS_OUTPUT.PUT_LINE('存在しないキー値を参照しました');END;/SET verify ON

SET serveroutput ONSET verify OFFDECLAREtype a_typeIS  TABLE OF VARCHAR2(10) INDEX BY binary_integer;  a a_type;BEGIN  a(5)  := 'five';  a(-3) := 'minus 3';  a(0)  := 'zero';  a(7)  := 'seven';  a(9)  := 'nine';  IF a.exists(2) THEN    DBMS_OUTPUT.PUT_LINE(A(2));  ELSE    DBMS_OUTPUT.PUT_LINE('存在しないキー値を参照しました');  END IF;END;/SET verify ON