def GetNewIssueStarrers(cnxn, services, issue_id, merge_into_iid):
  """Get starrers of current issue who have not starred the target issue."""
  source_starrers = services.issue_star.LookupItemStarrers(cnxn, issue_id)
  target_starrers = services.issue_star.LookupItemStarrers(
      cnxn, merge_into_iid)
  return set(source_starrers) - set(target_starrers)