Nested JsonObject properties are serialized as empty objects

[Maikkelinen]

Description:
Nested JsonObject values within track event properties are sent to Segment servers as empty objects {}, while the equivalent structure works correctly with the Swift SDK (analytics-swift).

Environment:

• analytics-kotlin version: 1.24.1 (also reproduced on 1.22.0)
• Android API: 35
• Kotlin: 2.0.21
• kotlinx.serialization: (bundled with SDK)
• Device: Pixel emulator (sdk_gphone64_arm64), Android 15

Steps to Reproduce:

  val props = buildJsonObject {
      putJsonObject("selected_values") {
          putJsonArray("key") {
              add(JsonPrimitive("value_1"))
              add(JsonPrimitive("value_2"))
          }
      }
      put("skipped", false)
  }
  // Log confirms correct structure:
  // {"selected_values":{"key":["value_1","value_2"]},"skipped":false}
  Log.i("Debug", "payload: $props")

  analytics.track("Tracking Event", props)

Expected Result:

Segment receives:

  {
    "properties": {
      "selected_values": {
        "key": ["value_1", "value_2"]
      },
      "skipped": false
    }
  }

Actual Result:

Segment raw data shows:

  {
    "properties": {
      "selected_values": {},
      "skipped": false
    },
    "context": {
      "protocols": {
        "omitted": ["selected_values.key"]
      }
    }
  }

The nested object arrives empty and the nested field appears in protocols.omitted.

Additional context:

• The JsonObject is correct in memory — logging .toString() before passing to analytics.track() shows the full nested structure
• We tried multiple approaches: buildJsonObject with putJsonObject/putJsonArray, JsonObject(map) constructor, and re-parsing via Json.parseToJsonElement() — all produce the same empty result on the server
• The identical event structure sent from analytics-swift (iOS) works correctly — the same Segment source and tracking plan receives the nested object with all data intact
• Flat properties (strings, booleans, numbers) work fine — only nested objects are affected