jbpm 7 rest api query task instances with additional parameter groups

Question

So what I want to do is to show tasks belonging to certain user group assigned to the task..

According to the doc(jbpm 6.4) from Redhat regarding querying task instances, I can use additional parameters: status, groups and user. I tried to use "groups". I thought it means "user group" assigned to the user task. (the 7.1 docs doesn't even have relevant information)

Adding parameter "status" ( ?status=Completed ) works, but "groups" has no effect on the result data set. I don't know why. Has the new version changed or the parameter itself need to be formatted or there is group ID instead of strings.

Here is the doc:

16.6. QUERYING TASKS

Use the following entry point: http://SERVER:PORT/kie-server/services/rest/server/queries/. To use pagination, use the page and pageSize parameters. The following list of endpoints contains additional parameters, if applicable:

[GET] tasks/instances/pot-owners Returns a list of tasks where the actual user is defined as a potential owner.

Additional parameters you can use: status, groups, user.

Note that the user filter is applicable only when the request is sent without authentication.

My query is like:

http://SERVER:PORT/kie-server/services/rest/server/queries/tasks/instances/pot-owners?groups=trainers

I also tried to dig into the source code, but I failed:

https://github.com/kiegroup/jbpm/tree/f70a465dd2621f5598f043631b8eb991142e05ba/jbpm-services/jbpm-kie-services/src/main/java/org/jbpm/kie/services/impl

Any help would be appreciated