[Kotlin] Models with "additionalProperties" result in invalid Kotlin code

Description

When using the kotlin-spring generator, OpenAPI models including additionalProperties are generated as invalid Kotlin code.

openapi-generator version

5.4.0 and 6.0.1

OpenAPI declaration file content or url

components:
  schemas:
    MyObject:
      type: object
      properties:
        value:
          type: string
      additionalProperties: true
      required:
        - value

...is generated into...

data class MyObject(

    @field:JsonProperty("value", required = true) val `value`: kotlin.String,
) : kotlin.collections.HashMap<String, kotlin.Any>{

}

Note the missing () after kotlin.collections.HashMap<String, kotlin.Any>.

Suggest a fix/enhancement

I'd propose the fix as just adding the missing () to the kotlin-spring's dataClass.mustache file, but I'm not sure if it should be fixed there or in the general Kotlin code for the variable being provided to the template.

Start with the kotlin-spring generator and its dataClass.mustache template, using the OpenAPI schema and generated Kotlin shown in the issue as the reproduction. Check whether the missing constructor parentheses belong in the template or the value supplied to it. Done means the additionalProperties model generates valid Kotlin code, with the relevant generator checks passing.