import com.atlassian.jira.event.type.EventDispatchOption
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.bc.issue.search.SearchService
import com.atlassian.jira.web.bean.PagerFilter

def customFieldObject = ComponentAccessor.customFieldManager.getCustomFieldObjectsByName("multi user")[0]
def issueManager = ComponentAccessor.issueManager
def searchService = ComponentAccessor.getComponent(SearchService)
def currentUser = ComponentAccessor.jiraAuthenticationContext.loggedInUser
def unlimitedFilter = PagerFilter.unlimitedFilter
def jql = "\"multi user\" in inactiveUsers()"
def query = searchService.parseQuery(currentUser, jql).query

def issues = searchService.searchOverrideSecurity(currentUser, query, unlimitedFilter).results // issues for earlier versions

issues.each {
    def issue = issueManager.getIssueObject(it.id)
    def activeUsers = issue.getCustomFieldValue(customFieldObject).findAll {it.active}
    issue.setCustomFieldValue(customFieldObject, activeUsers)
    issueManager.updateIssue(currentUser, issue, EventDispatchOption.ISSUE_UPDATED, false)
}