Jquery错误:未捕获的类型错误:无法读取未定义的属性“长度”。

I have a form to call ajax for back-end processing, all input will stored in table and will return 'success' to to notify user the submission is success. But I facing an issue during callback, input data can saved into table but the callback is halted with error below, I have no idea what is goes wrong, the same script was applied to another form (with different form field) are working fine.I have a form to call ajax for back-end process