Jira:ScriptRunner:Only Admins can change closed tickets

As a Behaviour:

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.security.roles.ProjectRoleManager

// Get the current user
def currentUser = ComponentAccessor.getJiraAuthenticationContext().getLoggedInUser()

def projectRoleManager = ComponentAccessor.getComponent(ProjectRoleManager)
def adminProjectRole = projectRoleManager.getProjectRole("Administrators")

//underlyingIssue.assignee

if (projectRoleManager.isUserInProjectRole(currentUser, adminProjectRole, underlyingIssue.getProjectObject())) { 
    getFieldByName("Description").setReadOnly(false)
    getFieldByName("Priority").setReadOnly(false)
} else {
    getFieldByName("Description").setReadOnly(true);
    getFieldByName("Priority").setReadOnly(true);
}