RestSharp's built-in JSON serializer serializes all of an object's properties, even if they're null or otherwise the default value. How can I make it skip these properties?
An alternative, you can use other json libraries (json.net, servicestack.text, etc.) which support ignoring null values to serialize it first:
RestRequest request = new RestRequest();
...
string jsonString = ThirdPartySerialization(jsonObject);
request.AddParameter("application/json", jsonString, ParameterType.RequestBody);