Confusion with setSerializationInclusion(Include.NON_NULL)

[midovlvn]

I'm confused with setup in "Usage section":

ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
mapper.registerModule(new JsonNullableModule());

Please take a look on the following snippet ( val=null is passed in JSON and in Map):

record A (JsonNullable<BigDecimal> val) {}
ObjectMapper objectMapper = new ObjectMapper().registerModule(new JsonNullableModule());

A a1 = objectMapper.readValue("{ \"val\" : null }", A.class);
System.out.println(a1);

HashMap hashMap = new HashMap();
hashMap.put("val", null);
A a2 = objectMapper.convertValue(hashMap, A.class);
System.out.println(a2);

Output is consistent

A[val=JsonNullable[null]]
A[val=JsonNullable[null]]

But with setup

ObjectMapper objectMapper = new ObjectMapper().registerModule(new JsonNullableModule())
        .setSerializationInclusion(JsonInclude.Include.NON_NULL);

Output is not consistent

A[val=JsonNullable[null]]
A[val=JsonNullable.undefined]

Well, time for questions:

1. I do not understand why you propose in "Usage" section setup .setSerializationInclusion(JsonInclude.Include.NON_NULL). It looks useless.
2. I do not understand how serialization setup may affect deserialization (objectMapper.convertValue is deserialization)