In our codebase, we have a class called OptionalOrUndefined

public class OptionalOrUndefined<T> {

  @Getter private final boolean defined;
  private final T value;

  public static <T> OptionalOrUndefined<T> optionalOfNullable(T value) {
    return new OptionalOrUndefined<>(true, value);
  }

  public static <T> OptionalOrUndefined<T> undefined() {
    return new OptionalOrUndefined<>(false, null);
  }

  public static <T> OptionalOrUndefined<T> undefinedIfNull(OptionalOrUndefined<T> property) {
    return property != null ? property : OptionalOrUndefined.undefined();
  }

  public <U> OptionalOrUndefined<U> map(Function<? super T, ? extends U> mapper) {

    Objects.requireNonNull(mapper);
    return isDefined()
        ? OptionalOrUndefined.optionalOfNullable(value != null ? mapper.apply(value) : null)
        : OptionalOrUndefined.undefined();
  }
}

I would like to create a patch endpoint which maps to fields with this type:

public record PatchVehicleRequest(
    Long vehicleId,
    @OptionalOrUndefinedMapper OptionalOrUndefined<String> vin,
    @OptionalOrUndefinedMapper OptionalOrUndefined<String> color,
    @OptionalOrUndefinedMapper OptionalOrUndefined<String> amountDoors) {

}

For this I had created a Deserializer and a custom annotation:

@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotationsInside
@JsonDeserialize(using = OptionalOrUndefinedDeserializer.class)
@JsonInclude(JsonInclude.Include.NON_NULL)
public @interface OptionalOrUndefinedMapper {
}

public class OptionalOrUndefinedDeserializer extends JsonDeserializer<OptionalOrUndefined<?>> {

  @Override
  public OptionalOrUndefined<?> deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException {
    JsonNode node = jsonParser.getCodec().readTree(jsonParser);

    if ( node.isMissingNode()) {
      return OptionalOrUndefined.undefined();
    } else if (node.isNull()) {
      return OptionalOrUndefined.optionalOfNullable(null);
    } else {
      String value = node.asText();
      return OptionalOrUndefined.optionalOfNullable(value);
    }
  }
}

But when calling the patch endpoint with following json:

{
  "vehicleId":5,
  "vin": null,
  "color": "test"
}

What happens is that vin and amountDoors stays null, instead of becoming a defined empty optional and an undefined object. Color is set to defined optional with value “test” as expected.