usergroup.massUpdate doesn't work with only rights parameter on 2.0.

This JSON request (only use rights parameter):
{"auth":"xxxxx","jsonrpc":"2.0","id":1,"method":"usergroup.massUpdate","params":{"usrgrpids":["13"],"rights":[

{"id":"2","permission":"3"}

]}}

Return:
"error":

{"code":-32500,"message":"Application error.","data":"Cannot perform update statement on table \"usrgrp\" without values."}

Same API request works well on 1.8.

If "name" parameter is included, the request is successful on 2.0
{"auth":"xxxxx","jsonrpc":"2.0","id":1,"method":"usergroup.massUpdate","params":{"usrgrpids":["13"],"name":"Linux Admins","rights":[

{"id":"2","permission":"3"}

]}}

{"usrgrpids"=>["13"]}