vyos.configdict: leaf_node_changed() must return empty dict when node is added

vyos@vyos# show interfaces pppoe
 pppoe pppoe10 {
+    access-concentrator asdfg
     authentication {
         password bar
         user foo
     }
     default-route force
     no-peer-dns
     source-interface eth0.202
 }

vyos@vyos# python3
Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from vyos.config import Config
>>> from vyos.configdict import get_interface_dict
>>> from vyos.configdict import leaf_node_changed
>>> conf = Config()
>>> base = ['interfaces', 'pppoe']
>>> tmp = get_interface_dict(conf, base, 'pppoe10')
>>> leaf_node_changed(conf, ['access-concentrator'])
>>> ['']

1 files changed, 3 insertions, 1 deletions

diff --git a/python/vyos/configdict.py b/python/vyos/configdict.py
index a0056a142..e15579b95 100644
--- a/python/vyos/configdict.py
+++ b/python/vyos/configdict.py
@@ -117,9 +117,11 @@ def leaf_node_changed(conf, path):
     D.set_level(conf.get_level())
     (new, old) = D.get_value_diff(path)
     if new != old:
+        if old is None:
+            return ['']
         if isinstance(old, str):
             return [old]
-        elif isinstance(old, list):
+        if isinstance(old, list):
             if isinstance(new, str):
                 new = [new]
             elif isinstance(new, type(None)):