@Override
        public Void timestampShape(TimestampShape timestampShape) {
            if (member.hasTrait(TimestampFormatTrait.ID)) {
                switch (member.expectTrait(TimestampFormatTrait.class).getFormat()) {
                    case EPOCH_SECONDS:
                        writer.writeInline(
                                "$T.ofEpochSecond($LL)",
                                Instant.class,
                                defaultValue.expectNumberNode().getValue().longValue());
                        return null;
                    case HTTP_DATE:
                        writer.writeInline(
                                "$T.from($T.RFC_1123_DATE_TIME.parse($S))",
                                Instant.class,
                                DateTimeFormatter.class,
                                defaultValue.expectStringNode().getValue());
                        return null;
                    default:
                        // Fall through on default
                        break;
                }
            }
            writer.write("$T.parse($S)", Instant.class, defaultValue.expectStringNode().getValue());
            return null;
        }
Adds default values to builder properties.
smithy-trait-codegen/src/main/java/software/amazon/smithy/traitcodegen/generators/BuilderGenerator.java