opm fails to serve FBC if cachedir not provided

opm serve fails with message:

Error: compute digest: compute hash: write tar: stat .: os: DirFS with empty root

4.12

100%

1. mkdir /tmp/catalog

2. using Dockerfile /tmp/catalog.Dockerfile based on 4.12 docs (https://access.redhat.com/documentation/en-us/openshift_container_platform/4.12/html-single/operators/index#olm-creating-fb-catalog-image_olm-managing-custom-catalogs
# The base image is expected to contain
# /bin/opm (with a serve subcommand) and /bin/grpc_health_probe
FROM registry.redhat.io/openshift4/ose-operator-registry:v4.12

# Configure the entrypoint and command
ENTRYPOINT ["/bin/opm"]
CMD ["serve", "/configs"]

# Copy declarative config root into image at /configs
ADD catalog /configs

# Set DC-specific label for the location of the DC root directory
# in the image
LABEL operators.operatorframework.io.index.configs.v1=/configs

3. build the image `cd /tmp/ && docker build -f catalog.Dockerfile .`

4. execute an instance of the container in docker/podman `docker run --name cat-run [image-file]`

5. error

Error: compute digest: compute hash: write tar: stat .: os: DirFS with empty root

opm generates cache in default /tmp/cache location and serves without error