code: def related_units(relid=None):
      
      relid = relid or relation_id()
      units_cmd_line = ['relation-list', '--format=json']
      if relid is not None:
          units_cmd_line.extend(('-r', relid))
      return json.loads(
          subprocess.check_output(units_cmd_line).decode('UTF-8')) or []
docs: A list of related units