[BUG] Kotlin DTO with object member not generated properly

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

openapi-generator version

7.2.0, don't know about previous versions as this was my first attempt

OpenAPI declaration file content or url

With this schema :

openapi: 3.0.0
paths:
info:
  title: Eixample API
  description: The API for the Eixample backend.
  version: 0.1.0
servers:
  - description: Development
    url: https://api.dev.eixample.dev
components:
  securitySchemes:
    bearer:
      type: http
      scheme: bearer
      bearerFormat: JWT
  schemas:
    Geozone:
      type: object
      properties:
        geoJson:
          type: object
          description: The definition of the geometry for the geozone.
          additionalProperties: true
        id:
          type: string
          description: The unique identifier for the geozone.
          format: uuid
      required:
        - geoJson
        - id

I obtain this class:

/**
 *
 * Please note:
 * This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
 * Do not edit this file manually.
 *
 */

@file:Suppress(
    "ArrayInDataClass",
    "EnumEntryName",
    "RemoveRedundantQualifierName",
    "UnusedImport"
)

package com.heetch.common.business.repositories.eixampleApi.dto

import com.heetch.common.business.repositories.eixampleApi.dto.AllowedLocation

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerialName
import kotlinx.serialization.Contextual

/**
 * 
 *
 * @param geoJson The definition of the geometry for the geozone.
 * @param id The unique identifier for the geozone.
 */
@Serializable

data class Geozone (

    /* The definition of the geometry for the geozone. */
    @Contextual @SerialName(value = "geoJson")
    val geoJson: kotlin.collections.Map<kotlin.String, kotlin.Any>,

    /* The unique identifier for the geozone. */
    @Contextual @SerialName(value = "id")
    val id: java.util.UUID,

Which causes an error on val geoJson: kotlin.collections.Map<kotlin.String, kotlin.Any> described as:

Serializer has not been found for type 'Any'. To use context serializer as fallback, explicitly annotate type or property with @Contextual

Generation Details

Gradle plugin task:

openApiGenerate {
    generatorName.set("kotlin")
    inputSpec.set("$rootDir/some.yaml")
    outputDir.set(generatedSourcesPath)
    packageName.set("some.package")
    modelPackage.set("some.package")
    configOptions.set(mapOf(
        "dateLibrary" to "java8",
        "collectionType" to "list",
        "serializationLibrary" to "kotlinx_serialization",
    ))
}

Steps to reproduce

Execute the openApiGenerate task

Related issues/PRs

Suggest a fix

Adding @Contextual to the second type of Map : kotlin.collections.Map<kotlin.String, @Contextual kotlin.Any> seems to fix the issue.

Start by reproducing the issue with the Gradle openApiGenerate task, using the Kotlin generator, kotlinx_serialization, and the provided schema. Trace how an object with additionalProperties becomes the generated Kotlin Map type; done means the generated DTO compiles without the kotlinx.serialization Any serializer error.