[loki-stack] memberlist can't be set to null

[bkk-bcd]

# from within loki-stack helm chart dir
❯ helm template --set loki.config.memberlist=null . | egrep memberlist
# Source: loki-stack/charts/loki/templates/service-memberlist.yaml
  name: RELEASE-NAME-loki-memberlist
      targetPort: memberlist-port
            - name: memberlist-port
# from within loki helm chart dir
❯ helm template --set config.memberlist=null . | egrep memberlist
(no output)