Can't serialize Kotlin Value class that has map inside

[kkocel]

Search before asking

• I searched in the issues and found nothing similar.
• I have confirmed that the same problem is not reproduced if I exclude the KotlinModule.
• I searched in the issues of databind and other modules used and found nothing similar.
• I have confirmed that the problem does not reproduce in Java and only occurs when using Kotlin and KotlinModule.

Describe the bug

I tried to serialize Kotlin value class, and failed with:

Cannot invoke "com.fasterxml.jackson.databind.JsonSerializer.serialize(Object, com.fasterxml.jackson.core.JsonGenerator, com.fasterxml.jackson.databind.SerializerProvider)" because "keySerializer" is null (through reference chain: com.paramount.snapshooter.pitstop.SerializationValueClassTest$TimestampedPerson["person"]->java.util.LinkedHashMap["id"])
com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "com.fasterxml.jackson.databind.JsonSerializer.serialize(Object, com.fasterxml.jackson.core.JsonGenerator, com.fasterxml.jackson.databind.SerializerProvider)" because "keySerializer" is null (through reference chain: com.paramount.snapshooter.pitstop.SerializationValueClassTest$TimestampedPerson["person"]->java.util.LinkedHashMap["id"])

To Reproduce

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import org.junit.jupiter.api.Test

class SerializationValueClassTest() {

    @Test
    fun `should serialize value class`() {

        val person = Person(
            mapOf(
                "id" to "123",
                "updated" to "2023-11-22 12:11:23",
                "login" to "2024-01-15",
            ),
        )

        val serialized2 = jacksonObjectMapper().writeValueAsString(
            TimestampedPerson(
                123L,
                Person(person.properties),
            )
        )

        val deserialized2 = jacksonObjectMapper().readValue<TimestampedPerson>(serialized2)

        assert(
            deserialized2 == TimestampedPerson(
                123L,
                Person(person.properties),
            )
        )
    }

    @JvmInline
    value class Person(
        val properties: Map<String, Any>,
    )

    data class TimestampedPerson(
        val timestamp: Long,
        val person: Person,
    )
}

Expected behavior

Value class shoud be serialized

Versions

Kotlin: 2.10
Jackson-module-kotlin: 2.17.1
Jackson-databind: 2.18.1

Additional context

No response

[cowtowncoder]

Quick note on this:

Jackson-module-kotlin: 2.17.1
Jackson-databind: 2.18.1

The general rule is that minor versions should match to avoid any incompatibilities. Although in this particular case order of dependencies is such that this should work (kotlin can depend on later databind versions; but not vice versa).

Still, I'd suggest trying this out with both Kotlin module and databind with latest published version, 2.18.2, to rule out possibility of issue being fixed since versions you use.

[kkocel]

@cowtowncoder I checked it with 2.18.2 and created https://github.com/kkocel/jackson-module-kotlin-873 with reproduction