'return None for SuccessResponse with no AX paramaters.'

def test_fromSuccessResponseWithoutExtension(self):

    args = {'mode': 'id_res', 'ns': OPENID2_NS}
    sf = [('openid.' + i) for i in args.keys()]
    msg = Message.fromOpenIDArgs(args)
    class Endpoint:
        claimed_id = 'http://invalid.'
    oreq = SuccessResponse(Endpoint(), msg, signed_fields=sf)
    r = ax.FetchResponse.fromSuccessResponse(oreq)
    self.failUnless((r is None), ('%s    is    not    None' % (r,)))
