public List<String> groupIds() {
        return data.groups()
            .stream()
            .map(OffsetFetchRequestGroup::groupId)
            .collect(Collectors.toList());
    }
Indicates that it is not possible to fetch consumer groups in batches with FetchOffset.
Instead consumer groups' offsets must be fetched one by one.
clients/src/main/java/org/apache/kafka/common/requests/OffsetFetchRequest.java