Can not do rollback

[xukai-ibm]

The API rollback_group(group_id=args.group_id, version=args.version, force=False) does not work well. My DC/OS version is 1.9.0.
I get an error of 400 :

Got HTTP 400: b'{"message":"Please specify data in JSON format","details":"No content to map due to end-of-input\\n at [Source: [B@59c504cb; line: 1, column: 0]"}'

my code is:

result = client.rollback_group(group_id=args.group_id, version=args.version, force=False)