how to add Automatically echo Assignees to the Collaborators Field

[Santhosh Vegolam]

Hello Team,

Our requirement is whenever issue is assigned to some one in new/To do status automatically to collaborators custom filed 

we are implemented to each and every transitions to add post function Copy Value From Other Field (JSU) it is working fine whenever move to other status only assignee will be added to collaborators field but not in initial status not happened automatically untill unless move the transition to other status we applied post function while create to new also   

So we want to be happen in the initial status also this should be done automatically when assignee changed or updated 

please suggest how to fix it if any possible through scripting we using script runner plugin also 

we are using Jira-7.9.2 standalone server application

Thanks!