diff.py

    for field in changed_bar_fields_whitelist:
        formatted_field_name = '_stashed_{}'.format(field)
        try:
            stashed_field = getattr(instance, formatted_field_name)
            current_field = getattr(instance, field)
            if current_field != stashed_field:
                changed.append(field)
        except AttributeError:
            pass