public static async Task<TwitterSuccess> AddUserToMyList(this IUserSession session, long listId,
string screenNameToAdd="", long userIdToAdd=0, string slug ="", string ownerScreenName = "", long ownerId = 0)
{
var parameters = new TwitterParametersCollection();
parameters.Create(list_id: listId, slug: slug, owner_id: ownerId, owner_screen_name: ownerScreenName, user_id: userIdToAdd, screen_name: screenNameToAdd);
return await session.PostAsync(TwitterApi.Resolve("/1.1/lists/members/create.json"), parameters)
.ContinueWith(c => c.MapToTwitterSuccess());
}