Dart Object -> JSON String failing to convert to JSON
I think your problem is that you use print(req.toString());. Have you tried to do this:
objectToJson(req).then((jsonStr) => print(jsonStr)); Maybe this gives you a json string.
I personally feel like you actually SHOULD provide a toJson/toObject method because you have full control over what is serialized and how it is serialized (e.g. exclude private fields, null values, ...).
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Because you use extends JsonObject toString() returns an empty map.
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https://code.google.com/p/dart/issues/detail?id=6490 doesn't look like it is supported well. But then you can't use the json_object package anyway.
Exception: Uncaught Error: Class '_LocalClassMirror' has no instance getter 'getters'. This should be because the package requires experimental mirror features.
Using JSON.encode you cannot put an object into there. See https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:convert.JsonCodec#id_encode :
Either you specify the second parameter or implement .toJson().