Ab und zu NullReferenceException ( List, Class )

    public class PlayerManager{
        public class PlayerData{
            string[] PlayerDataString = { "" };
            int[] PlayerDataInt = { 0 };
            Socket PlayerDataSocket;
            /* === PlayerDataString ===
             * [0] PlayerName
             * 
             * 
             * */
            /* === PlayerDataInt === 
             * [0] Session ID
             * 
             * */
            public void SetName(string PlayerName){this.PlayerDataString[0] = PlayerName;}
            public void SetSocket(Socket handler){this.PlayerDataSocket = handler;}
            public void SetSessionID(int SessionID){this.PlayerDataInt[0] = SessionID;}
            public Socket GetSocket(){return this.PlayerDataSocket;}
            public int GetSessionID() { return this.PlayerDataInt[0]; }
        }
        private static List<PlayerData> PlayerDataList = new List<PlayerData>();
        public static void CreatePlayerData(Socket PlayerHandler,string PlayerName,int SessionID){
            try{
                PlayerData CreateNewPlayer = new PlayerData();
                //--------------------------------------------
                CreateNewPlayer.SetName(PlayerName);
                CreateNewPlayer.SetSessionID(SessionID);
                CreateNewPlayer.SetSocket(PlayerHandler);
                //--------------------------------------------
                PlayerDataList.Add(CreateNewPlayer);
            }
            catch (Exception ex) { GameConsole.WriteConsoleGameParams(System.ConsoleColor.Red, $"ERROR GetPlayerBySocket()", ex.ToString()); }
        }
        public static PlayerData GetPlayerBySocket(Socket handler){
            PlayerData returnPlayerData = null;
            try {
                for (int i = 0; i <= PlayerDataList.Count-1; i++) {
                    if (PlayerDataList[i].GetSocket() == handler){
                        returnPlayerData = PlayerDataList[i];
                        break;
                    }
                }
                return returnPlayerData;
            }
            catch (Exception ex) { GameConsole.WriteConsoleGameParams(System.ConsoleColor.Red, $"ERROR GetPlayerBySocket()", ex.ToString()); return returnPlayerData; }
        }
    }

        public static void IncommingPacket(Socket handler,byte[] PacketByte){
            try{
                PlayerManager.PlayerData PacketPlayer = PlayerManager.GetPlayerBySocket(handler);
                    if (PacketPlayer.GetSessionID() == 0){
                        string SessionPacket =
GameCrypto.DecryptCustomParameter(PacketByte);
                        string[] SessionParts = SessionPacket.Split(' ');
                        if (SessionParts.Length < 2 || !SessionParts.Any()){
                            return;
                        }
                        int SessionID;
                        if (int.TryParse(SessionParts[1].Split('\\').FirstOrDefault(), out SessionID))
                        {
                            Console.WriteLine("Test .. Session hat sich verbunden: " + SessionID);
                        }
                    }
            }
            catch (Exception ex) { GameConsole.WriteConsoleGameParams(System.ConsoleColor.Red, $"ERROR IncommingPacket", ex.ToString()); }
        }

if (PacketPlayer.GetSessionID() == 0){