Deserializing into Optionals not working with @Introspected

[cweinberger]

Expected Behavior

When deserializing JSON into a POJO, Optionals should be handled properly to allow detecting the absence/presence of a value (as needed on PATCH endpoints for example, where you want to differentiate between null and absence of a value).

This works fine, until I add @Introspected annotation to the POJO (which is required for Validations etc as well).

Example POJO

@Introspected
data class TestPojo(
    val field1: Optional<String>? = null,
    val field2: Optional<String>? = null
)

JSON

val output1 = objectMapper.readValue("{\"field1\": \"value1\", \"field2\": \"value2\"}", TestPojo::class.java)
val output2 = objectMapper.readValue("{\"field1\": null, \"field2\": \"value2\"}", TestPojo::class.java)
val output3 = objectMapper.readValue("{}", TestPojo::class.java)

Output

assert(output1.field1?.get() == "value1")
assert(output1.field2?.get() == "value2")

assert(output2.field1!!.isEmpty)
assert(output2.field2?.get() == "value2")

assert(output3.field1 == null)
assert(output3.field2 == null)

Actual Behaviour

When @Introspected is not used on the POJO, all is fine; however, when adding @Introspected to the POJO, both null and absent values are mapped to Optional.empty()

Output

assert(output1.field1?.get() == "value1") // ✅
assert(output1.field2?.get() == "value2") // ✅

assert(output2.field1!!.isEmpty) // ✅
assert(output2.field2?.get() == "value2") // ✅

assert(output3.field1 == null) // ❌ - Optional.empty()
assert(output3.field2 == null) // ❌ - Optional.empty()

Steps To Reproduce

I added tests in the linked sample project (DemoTest.kt)

Environment Information

macOS 14.4.1
JDK 17

Example Application

https://github.com/cweinberger/micronaut-optionals-introspected-demo

Version

4.3.6

[sdelamo]

@cweinberger if you are using Micronaut Jackson Databind you could use https://github.com/OpenAPITools/jackson-databind-nullable for supporting thing such as JSON Merge Patch