OPENBALENA_VPN_CA_CHAIN not set

When I run :
./scripts/compose up -d

I get the nest warning :
WARNING: The OPENBALENA_VPN_CA_CHAIN variable is not set. Defaulting to a blank string.
Starting openbalena_redis_1_7c91407d8700 … done
Starting openbalena_db_1_a3d4e40e4e00 … done

Any ideas why this warning?

Thank you