How to get the mutable issue under Scriptrunner Custom scheduled job

Hi team,

I want to assign tickets to Service desk agents based on my script and I want to run that script as a Custom scheduled job ,Can anyone help me out ,how to get mutable issue in Custom scheduled job script.

Jira Server version -8.4.1

Getting below error :2020-05-18 15:29:18,048 ERROR [jobs.AbstractCustomScheduledJob]: *************************************************************************************
2020-05-18 15:29:18,049 ERROR [jobs.AbstractCustomScheduledJob]: Script job: ‘Auto assign ticket based on existing assigned tickets’ failed
groovy.lang.MissingPropertyException: No such property: issue for class: Script60