@Override
        protected Void getDefault(Shape shape) {
            throw new CodegenException(String.format(
                    "Unexpected member %s of type %s",
                    shape.getId(),
                    shape.getType()));
        }
@return returns the suffix that will be applied to the parent shape's link
        id to form this member listing's link id.
smithy-docgen/src/main/java/software/amazon/smithy/docgen/generators/MemberGenerator.java