docker.io upgrade to 20.10.2-0ubuntu1~20.04.2 failed

Updating docker.io from focal-proposed (19.03.8-0ubuntu1.20.04.2 -> 20.10.2-0ubuntu1~20.04.2) fails with this error message:

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

After adding "set -x" to "/var/lib/dpkg/info/docker.io.postinst":

# dpkg --configure -a
Setting up docker.io (20.10.2-0ubuntu1~20.04.2) ...
+ . /usr/share/debconf/confmodule
+ [ ! ]
+ PERL_DL_NONLAZY=1
+ export PERL_DL_NONLAZY
+ [ ]
+ exec /usr/share/debconf/frontend /var/lib/dpkg/info/docker.io.postinst configure 19.03.8-0ubuntu1.20.04.2
+ . /usr/share/debconf/confmodule
+ [ ! 1 ]
+ [ -z ]
+ exec
+ [ ]
+ exec
+ DEBCONF_REDIR=1
+ export DEBCONF_REDIR
+ [ -z 19.03.8-0ubuntu1.20.04.2 ]
+ dpkg --compare-versions 19.03.8-0ubuntu1.20.04.2 le-nl 1.11.2~ds1-1
+ command -v zfs
+ [ -x /usr/sbin/zfs ]
+ modinfo zfs
+ zfs mount
+ awk $2=="/" {print $1}
+ cut -d/ -f1
+ rpool=rpool
+ [ -n rpool ]
+ findmnt -n -o SOURCE /var/lib/docker
+ dockermnt=rpool/var/lib/docker
+ echo rpool/var/lib/docker
+ grep -qE ^$|/ROOT/
+ dpkg --compare-versions 19.03.8-0ubuntu1.20.04.2 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

If it's any help, my /var/lib/docker is zfs, but it's not under rpool/ROOT:

TARGET SOURCE FSTYPE OPTIONS
/ rpool/ROOT/ubuntu_uryi4p zfs rw,relatime,xattr,posixacl
├─/var/lib rpool/ROOT/ubuntu_uryi4p/var/lib zfs rw,noatime,xattr,posixacl
│ ├─/var/lib/apt rpool/ROOT/ubuntu_uryi4p/var/lib/apt zfs rw,noatime,xattr,posixacl
│ ├─/var/lib/docker rpool/var/lib/docker zfs rw,noatime,xattr,posixacl