Docker folder removed after removed Docker package in Synology

I was changing harddisk in Synology DSM 7 in the volume with Docker package installed by recreating the volume, it requires docker package to be removed. I thought the docker folder (/volumeX/docker) might not removed, so backed up the container images into docker folder. But I was wrong, the docker folder was removed.

The docker folder was created by Docker package, which can be moved to other volume after stopped Docker package. I didn't see any data in it, and I don't know what the usage of this folder is and it is zero in size.