Modifying server scripted field to work in cloud, get Parent summary

[Deleted user]

We have this Scriptrunner scripted field that checks if issue has a parent, and if so gets the summary. How would I go about modifying this to work in Jira Cloud? Thank you for any help

def parent = issue.getParentObject();
if (!parent){
return
}
else{
parent.getSummary();
}