trackVerified returns error

Hi
I have a problem with `Radar.trackVerified(beacons: false)` because it returns following result with exception:
```
{
   "error":"java.lang.NullPointerException: Attempt to invoke virtual method 'org.json.JSONObject io.radar.sdk.model.RadarVerifiedLocationToken.toJson()' on a null object reference"
}
```

I use `flutter_radar: ^3.12.0`
