[DAV] Fix characters handling

aleksis/core/util/dav_handler/base.py

@@ -34,7 +34,7 @@ class ElementHandler(RegistryObject, is_registry=True):
         self.request = request
         self.parent = parent
         self.attrs = attrs
-        self.content = None
+        self.content = ""
         if invisible is not None:
             self.invisible = invisible
         else:
@@ -191,7 +191,7 @@ class DAVRequest(ElementHandler, ContentHandler):
     def characters(self, content):
         """Handle content of an XML element."""
 
-        self.current_object.content = content
+        self.current_object.content += content
 
 
 class DAVMultistatus: