Server Error in '/' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:



Line 241:            lobbyViewModel.lobby.name = lobbyViewModel.name;
Line 242:            lobbyViewModel.lobby.category.id = categoryId;
Line 243:            lobbyViewModel.lobby.isStarted = false;
Line 244:            lobbyClient.CreateLobby(lobbyViewModel.lobby);

[DataContract(IsReference = true)]
    public class Category
    {
        [DataMember]
        public int id { get; set; }
        [DataMember]
        public string name { get; set; }
        [DataMember]
        public int amount { get; set; }
        [DataMember]
        public Quiz quiz { get; set; }
        [DataMember]
        public List<Question> question { get; set; }

        public Category()
        {
            question = new List<Question>();
        }
    }

public class Lobby
    {
        [DataMember]
        public int id { get; set; }
        [DataMember]
        public string name { get; set; }
        [DataMember]
        public Category category { get; set; }
        [DataMember]
        public bool isStarted { get; set; }
    }

public class LobbyViewModel
{
    public LobbyReference.Lobby lobby { get; set; }
    public List<LobbyReference.Lobby> lobbies { get; set; }

    public LobbyViewModel()
    {
        lobby = new LobbyReference.Lobby();
        lobbies = new List<LobbyReference.Lobby>();
    }

    public int id { get; set; }
    public string name { get; set; }
    public int categoryId { get; set; }
    public bool isStarted { get; set; }
}

public void CreateLobby(Lobby lobby)
        {
            TransactionOptions options = new TransactionOptions();
            options.IsolationLevel = System.Transactions.IsolationLevel.Serializable;

            using (TransactionScope scope = new TransactionScope(TransactionScopeOption.Required, options))
            {
                using (var conn = new SqlConnection(connectionString))
                {
                    using (SqlCommand command = conn.CreateCommand())
                    {
                        conn.Open();
                        command.CommandText = "INSERT INTO Lobby(name, categoryId, isStarted)VALUES(@name, @categoryId, @isStarted)";
                        command.Parameters.Add("name", SqlDbType.NVarChar).Value = lobby.name;
                        command.Parameters.Add("categoryId", SqlDbType.Int).Value = lobby.category.id;
                        command.Parameters.Add("isStarted", SqlDbType.Bit).Value = lobby.isStarted;
                        command.ExecuteNonQuery();
                    }
                    scope.Complete();
                    conn.Close();
                }
            }
        }

// THIS IS MY WCF REFERENCE WHERE I CAN CALL MY METHODS FROM
private LobbyServiceClient lobbyClient = new LobbyServiceClient();

public ActionResult Lobby(int categoryId)
    {
        LobbyViewModel lobbyViewModel = new LobbyViewModel();
        lobbyViewModel.lobbies = lobbyClient.GetAllLobbiesWithCategoryId(categoryId);
        lobbyViewModel.categoryId = categoryId;
        return View(lobbyViewModel);
    }

    public ActionResult CreateLobby(int categoryId)
    {
        LobbyViewModel lobbyViewModel = new LobbyViewModel();
        lobbyViewModel.categoryId = categoryId;
        return View(lobbyViewModel);
    }

    [HttpPost]
    public ActionResult CreateLobby(LobbyViewModel lobbyViewModel, int categoryId)
    {
        lobbyViewModel.lobby.name = lobbyViewModel.name;
        lobbyViewModel.lobby.category.id = categoryId;
        lobbyViewModel.lobby.isStarted = false;
        lobbyClient.CreateLobby(lobbyViewModel.lobby);
        return RedirectToAction("Lobby");
    }