mv: cannot stat '/var/lib/docker.migrating/*': No such file or directory

Adding set -x to the postinst section, we see this:
Setting up docker.io (19.03.11-0ubuntu1) ...
+ modinfo zfs
+ zfs mount
+ + awkcut -d/ -f1
 $2=="/" {print $1}
+ rpool=rpool
+ [ -n rpool ]
+ findmnt -n -o SOURCE /var/lib/docker
+ dockermnt=rpool/docker
+ echo rpool/docker
+ grep -qE ^$|/ROOT/
+ dpkg --compare-versions 19.03.8-0ubuntu1 le-nl 19.03.8-0ubuntu2
+ mv /var/lib/docker.migrating/* /var/lib/docker/
mv: cannot stat '/var/lib/docker.migrating/*': No such file or directory
dpkg: error processing package docker.io (--configure):
 installed docker.io package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 docker.io

This bug was fixed in the package docker.io - 19.03.11-0ubuntu2

---------------
docker.io (19.03.11-0ubuntu2) groovy; urgency=medium

  [ Jean-Baptiste Lallement ]
  [ Didier Roche ]
  * Fix postinst docker migration if people migrated to new layout manually
    before installing migrated version. (LP: #1882942)
  * Ensure new install creates <pool>/var/lib/docker if any of their history is
    a ZFS installation.

 -- Didier Roche <email address hidden> Wed, 10 Jun 2020 15:25:30 +0200

Copying over my workaround from https://github.com/ubuntu/zsys/issues/170#issuecomment-826359558 :

Just to chime in, I've been having the same issue myself.
Following @ddnexus's [analysis of the issue](https://github.com/ubuntu/zsys/issues/170#issuecomment-715901655_), the workaround is rather simple:
```
sudo mkdir /var/lib/docker.migrating
echo 'dummy' | sudo tee /var/lib/docker.migrating/workaround.txt
```
this will allow the `stat '/var/lib/docker.migrating/*'` to not fail with an error.

After the successful `apt update docker.io` run, you can remove the workaround dummy file:
```
sudo rm /var/lib/docker/workaround.txt
```

Hope others find this useful.