Execute request with callbacks

RestClientExecuteWithCallback.cs

public static class RestClientExecuteWithCallback
{
    public static Task ExecuteWithCallbacks<T>(this IRestClient client, IRestRequest request, Action<T> success, Action<Exception, string> failure)
    {
        return ExecuteWithCallbacks(client, request, success, failure, null);
    }

    public static Task ExecuteWithCallbacks<T>(this IRestClient client, IRestRequest request, Action<T> success, Action<Exception, string> failure, Action<IRestResponse, string> requestFailure)
    {
        if (success == null)
            throw new ArgumentNullException("success");
        if (failure == null)
            throw new ArgumentNullException("failure");

        var execTask = client.Execute<T>(request);
        execTask
            .ContinueWith(
                t =>
                {
                    var result = t.Result;
                    if (result.Data == null)
                    {
                        if (requestFailure != null)
                            requestFailure(t.Result, "Result data is null");
                        else
                            failure(new NullReferenceException(), "Result data is null");
                    }
                    else
                        success(result.Data);
                },
                TaskContinuationOptions.OnlyOnRanToCompletion);
        execTask
            .ContinueWith(
                t =>
                {
                    var exception = t.Exception.InnerException;
                    failure(exception, exception.Message);
                },
                TaskContinuationOptions.OnlyOnFaulted);
        return execTask;
    }
}