input_type class name is not displayed in error message when message_list_attr is not a mutable sequence

[AMontagu]

this code in proto_serializers.py:

repeated_message = getattr(message, message_list_attr, "")
        if not isinstance(repeated_message, MutableSequence):
            error_message = self.default_error_messages["not_a_list"].format( # TODO not working anymore for custome input_type
                input_type=repeated_message.__class__.__name__
            )
            raise ValidationError(
                {api_settings.NON_FIELD_ERRORS_KEY: [error_message]}, code="not_a_list"
            )

Work but input_type=repeated_message.class.name is not correctly printed