How to remove data in persist

[sculove]

Description

a persist couldn't remove previous data.
and it couldn't update null or undefined or ""

Steps to check or reproduce

AS-IS

$.persist("key", { val : 10 }); // { val: 10 }
$.persist("key", null); // { val: 10 }
$.persist("key", undefined); // { val: 10 }
$.persist("key", ""); // { val: 10 }

TO-BE

$.persist("key", { val : 10 }); // { val: 10 }
$.persist("key", null); // null
$.persist("key", undefined); // undefined
$.persist("key", ""); // ""