StringContainer.add_from_etree fails for empty node

[notEvil]

Hi,

a perfectly valid invoice may contain for instance <IncludedNote><Content/></IncludedNote>. Container.add fails in this case as root.text is None. The following solves this issue:

--- models/container.py.orig	2024-12-11 10:20:20.833947854 +0100
+++ models/container.py	2024-12-11 10:20:24.930598120 +0100
@@ -91,4 +91,5 @@
         el._text = child
 
     def add_from_etree(self, root):
-        self.add(root.text)
+        if (_text := root.text) is not None:
+            self.add(_text)