get vitrage topology show with filter and default root

I use the cli:
vitrage topology show --filter '{"and": [{"==": {"category": "RESOURCE"}},{"==": {"is_deleted": false}},{"==": {"is_placeholder": false}},{"==": {"type": "nova.instance"}}]}'
I only want to show the instance with no specified root, so the root is default `openstack.cluster`

But from the code, see https://github.com/openstack/vitrage/blob/master/vitrage/graph/algo_driver/networkx_algorithm.py#L48
We first to match the root_data to the query conditions. If not matched, it returns.

So if i only want to query the instance, but with the default root `openstack.cluster`, will it return not match?
Should it be a mandatory option that we should specify a instance as root if we query with the filter instance??