[erp5_core] DiffTool: Raise error in case the selection for diff in a listbox...

[erp5_core] DiffTool: Raise error in case the selection for diff in a listbox has object not equal to 2

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_diff/Base_getObjectDiffList.py

@@ -30,6 +30,9 @@ if first_path is None and second_path is None:
   # create diff.
   if list_selection_name is not None:
     selected_obj_list = portal.portal_selections.getSelectionCheckedValueList(selection_name=list_selection_name)
+    # Check if the number of selected object is 2 only. otherwise raise an error
+    if len(selected_obj_list) != 2:
+      raise ValueError('Please select accurately 2 objects.')
     object_revision_list.extend(selected_obj_list)
   else:
     # Return an empty list here. This would be the case when we first access