docs: def get_columns_diff(changes):
      """Add the changed columns as a diff attribute.
  
      - changes: a list of changes (get_model_changes query.all())
  
      Return: the same list, to which elements we added a "diff"
      attribute containing the changed columns. Diff defaults to [].
      """
      for change in changes:
          change.diff = []
          elt_changes = change.get_changes()
          if elt_changes:
              change.diff = elt_changes.columns
  
      return changes