Come si utilizza una query geospaziale nel driver 2.1 MongoDB C#?

ecco come lo faccio da parte mia:

    public IQueryable<TEntity> FindNear<TEntity>(string collectionName, Expression<Func<TEntity, object>> field, double longitude, double latitude, double maxDistanceInKm) where TEntity : IEntity
    {
        var collection = database.GetCollection<TEntity>(collectionName);
        var point = GeoJson.Point(GeoJson.Geographic(longitude, latitude));
        var filter = Builders<TEntity>.Filter.Near(field, point, maxDistanceInKm * 1000);
        return collection.Find(filter).ToList().AsQueryable();
    }