Comment 1 for bug 1942930

Yes. Looks like you discovered a bug here.
It works if you unset an "interface subtree", e.g.:
$ sudo netplan set network.bridges.br54=null

But apparently not if you delete a whole set of devices, that might be spread across a set of YAML files (like network.bridges=null, network=null).

I can reproduce the issue with a simple unit-test in `test_clie_get_set.py` and we should fix it.

    def test_set_delete_subtree(self):
        with open(self.path, 'w') as f:
            f.write('''network:\n version: 2\n renderer: NetworkManager
  ethernets:
    eth0: {addresses: [1.2.3.4/24]}''')
        ret = self._set(['network.ethernets=null'])
        print(ret, flush=True) # debugging
        self.assertTrue(os.path.isfile(self.path))
        with open(self.path, 'r') as f:
            out = f.read()
            print(out, flush=True) # debugging
            self.assertIn('network:\n', out)
            self.assertIn(' version: 2\n', out)
            self.assertIn(' renderer: NetworkManager\n', out)
            self.assertNotIn('ethernets:', out)