docs: def relation_call(method, relation_name=None, flag=None, state=None, *args):
      """Invoke a method on the class implementing a relation via the CLI"""
      if relation_name:
          relation = relation_from_name(relation_name)
          if relation is None:
              raise ValueError('Relation not found: %s' % relation_name)
      elif flag or state:
          relation = relation_from_flag(flag or state)
          if relation is None:
              raise ValueError('Relation not found: %s' % (flag or state))
      else:
          raise ValueError('Must specify either relation_name or flag')
      result = getattr(relation, method)(*args)
      if isinstance(relation, RelationBase) and method == 'conversations':
          # special case for conversations to make them work from CLI
          result = [c.scope for c in result]
      return result