A null gender property throws an exception when calling ToResult<T>

[mattio]

While I was trying out some simple requests I found that a profile without a gender throws the following exception in the ToResult method of the Extensions class:

An unhandled exception of type 'Newtonsoft.Json.JsonSerializationException' occurred in Newtonsoft.Json.dll

Additional information: Error converting value {null} to type 'ValidicCSharp.Model.GenderType'. Path 'gender', line 1, position 66.

The error was triggered by this code:

var client = new Client();
var command = new Command()
    .AuthenticationToken(user.ValidicUserAccessToken)
    .GetInformationType(CommandType.Profile);

var json = client.PerformCommand(command);
var profile = json.ToResult<Profile>();

The JSON in this scenarios was:

{
  "profile": {
    "_id": "999999999999",
    "uid": "0123456789",
    "gender": null,
    "location": null,
    "country": null,
    "birth_year": null,
    "height": null,
    "weight": null,
    "devices": {
      "fitbit": {
        "111111111": {
          "battery": "High",
          "device_version": "Flex",
          "id": "111111111",
          "last_sync_time": "2017-02-25T09:05:53.000",
          "type": "TRACKER"
        }
      }
    },
    "applications": []
  }
}

I worked around this by making GenderType on Profile nullable. I did not submit a pull request because I'm not sure if that's how you would want that handled for all customers.