A PHP Error was encountered

Severity: Notice

Message: Undefined index: HTTP_USER_AGENT

Filename: helpers/common_helper.php

Line Number: 22

Backtrace:

File: /data/home/qxu1635850490/htdocs/project/helpers/common_helper.php
Line: 22
Function: _error_handler

File: /data/home/qxu1635850490/htdocs/project/controllers/Product.php
Line: 23
Function: is_mobile

File: /data/home/qxu1635850490/htdocs/index.php
Line: 324
Function: require_once