Comment 11 for bug 1943120

I Tested netplan.io 0.103-0ubuntu5~20.04.2 inside a fresh Focal LXD container:
$ lxc launch ubuntu-daily:focal ff
$ lxc exec ff bash

=> Enabled focal-proposed & installed/upgraded netplan.io

root@ff:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.103-0ubuntu5~20.04.2
ii netplan.io 0.103-0ubuntu5~20.04.2
root@ff:~# netplan set network.bridges.br54.dhcp4=false
root@ff:~# netplan get # check that br54 is present
network:
  bridges:
    br54:
      dhcp4: false
  ethernets:
    eth0:
      dhcp4: true
root@ff:~# netplan apply
root@ff:~# ip link show br54 && echo OK
3: br54: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 06:0f:64:90:38:53 brd ff:ff:ff:ff:ff:ff
OK
root@ff:~# mkdir -p /tmp/np_backup/etc/ && cp -r /etc/netplan /tmp/np_backup/etc/
root@ff:~# netplan set network.bridges.br54=null
root@ff:~# netplan get # check that br54 is NOT present
network:
  ethernets:
    eth0:
      dhcp4: true
netplan apply --state /tmp/np_backup
root@ff:~# ip link show br54 && echo ERROR
Device "br54" does not exist.

In accordance with https://wiki.ubuntu.com/NetplanUpdates I'm also attaching the full autopkgtest logs for those builds:
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_amd64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_arm64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_armhf.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_ppc64el.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_s390x.log