Jackson added getAbsentValue to its API in version 2.13, which is used when a field is absent. The current version of JsonNullableDeserializer, however, does not implement this method. This results in getNullValue being called, which in turn creates invalid deserialization results.

As the latest versions of Spring Boot use Jackson version > 2.13, this library is essentially unusable in its current form when it comes to new/up to date projects.

See FasterXML/jackson-databind#3214.