BusinessTemplate: Installed business template may be empty. Don't assume that it is not empty.

product/ERP5/Document/BusinessTemplate.py

@@ -2782,8 +2782,11 @@ class PortalTypeAllowedContentTypeTemplateItem(BaseTemplateItem):
     force = kw.get('force')
     installed_bt = kw.get('installed_bt')
     if installed_bt is not None:
-      old_objects = getattr(installed_bt,
-                            self.business_template_class_property)._objects
+      item = getattr(installed_bt, self.business_template_class_property, None)
+      if item is not None:
+        old_objects = item._objects
+      else:
+        old_objects = {}
     else:
       old_objects = {}
     for key in set(self._objects.keys()).union(old_objects.keys()):