[QUESTION] WriteNulls + Filter

[samuelAndalon]

IHello from graphql-kotlin!. I am currently exploring the usage of fastjson2 as replacement for jackson, our benchmarks are showing impressive results when comparing jackson with fastjson2.

Currently I am facing an issue where i need to partially write and not write null values, consider this data class and its @JsonInclude annotation

@JsonInclude(JsonInclude.Include.NON_NULL)
data class GraphQLResponse(
    val data: Map<String, Any?>? = null,
    val errors: List<GraphQLServerError>? = null,
    val extensions: Map<String, Any?>? = null,
)

the errors field needs to be included if and only if its a NON NULL value, however, if the data map contains null values those need to be serialized,

in order words, this object

val toSerialize = GraphQLResponse(
  data = mapOf(
    "foo" to mapOf(
       "bar" to 1
       "bar2" to null
    ),
    "other" to "something",
    "baa" to null
  ),
  errors = null
  extensions = null
)

Should be serialized as:

{
   "data": {
      "foo": {
        "bar": 1,
        "bar2": null
      },
      "other": "something",
      "baa": null
   }
}

errors and extensions fields not included in top level fields, data field contains the JSON representation of its type Map<String, Any?>, and null values are included.

Currently i was able to do this using a combination of a PropertyPreFilter and a JsonWriter feature

val filter = PropertyPreFilter { _, source, name ->
  when {
    source is GraphQLResponse && name == "errors" -> source.errors != null
    else -> true
  }
}

JSON.toJSONString(toSerialize, filter, JSONWriter.Feature.WriteNulls)

is there a way to to this in a different way without filters ?