Support flattening of dynamic properties in Map<String, Any> with proper serialization and introspection

[betulince]

Issue description

Expected Behavior

I'm trying to wrap a Map<String, Any> inside a Parameters class to be used as part of a JobRequest. The goal is to deserialize dynamic JSON objects with arbitrary fields into this map and serialize them back as a flattened structure like:

{
  "parameters": {
    "foo": "bar",
    "baz": 42
  }
}

I expected to be able to achieve this by using a simple wrapper around a map, similar to Jackson's @JsonAnyGetter/@JsonAnySetter, or via Micronaut annotations such as @Serdeable, @SerdeImport, or @SerdeConfig.

Actual Behavior

Despite attempting the above approaches, I encountered either of the following:

• Runtime error: No serializable introspection present for type Parameters
• Or the structure is serialized with an unwanted extra layer (parameterValues) like:

{
  "parameters": {
    "parameterValues": {
      "foo": "bar",
      "baz": 42
    }
  }
}

Additionally, using alternatives such as JsonNode or JsonObject instead of Map<String, Any> also resulted in bean introspection errors.

Steps To Reproduce

You can reproduce this with the sample app and failing test provided here:
sample application

Clone the repository and run the test to observe the error.

Environment Information

• Micronaut Version: 3.10.1
• Kotlin version: 1.6.21

Additional Notes

This issue is blocking for use cases where DTOs need to accept flexible, dynamic request bodies without predefining the schema, and respond with the same shape.

If possible, a mechanism similar to Jackson’s @JsonAnyGetter would be ideal for clean flattening.

[dstepanov]

This should be the annotation processor dependency:
implementation("io.micronaut.serde:micronaut-serde-processor")

[dstepanov]

Or KAPT / KSP

[betulince]

I tried adding implementation("io.micronaut.serde:micronaut-serde-jackson") and annotationProcessor("io.micronaut.serde:micronaut-serde-processor"), and also tried using kapt as an annotation processor, but I'm still seeing the same serialization error.