@Override
        public Void memberShape(MemberShape shape) {
            if (shape.hasTrait(IdRefTrait.ID)) {
                toStringMapper();
            } else {
                model.expectShape(shape.getTarget()).accept(this);
            }
            return null;
        }
Determines how to map a shape to a node.
smithy-trait-codegen/src/main/java/software/amazon/smithy/traitcodegen/generators/ToNodeGenerator.java