Invalid warning about mandatory class parameters without defaults

Section 11.9 of  the style guide specifies that "sane defaults SHOULD be provided for optional parameters". It only mentions defaults for **optional** parameters. It does not mention defaults for mandatory parameters.

The example diff at the bottom of section 11.9 includes a mandatory paramter without a default.

The relevant check was added in 76b4c4a0ba9e49fe2c62995a303f3033ff494f25.