Disconnecting connId=0 to prevent exploits from an Exception in MessageHandler

I’m working with Steam and got an error about which I can’t find anything. I attach an error and a screenshot of the code.

Disconnecting connId=0 to prevent exploits from an Exception in MessageHandler: NullReferenceException Object reference not set to an instance of an object

at CustomNetworkManager.OnServerAddPlayer (Mirror.NetworkConnection conn) [0x00048] in C:\Users\Kirill\SteamMultiplayerGame\Assets\Scripts\CustomNetworkManager.cs:20

at Mirror.NetworkManager.OnServerAddPlayerInternal (Mirror.NetworkConnection conn, Mirror.AddPlayerMessage msg) [0x00076] in C:\Users\Kirill\SteamMultiplayerGame\Assets\Mirror\Runtime\NetworkManager.cs:1159

at Mirror.MessagePacking+<>c__DisplayClass7_0`2[T,C].g__Wrapped|0 (C conn, T msg, System.Int32 _) [0x00000] in C:\Users\Kirill\SteamMultiplayerGame\Assets\Mirror\Runtime\MessagePacking.cs:136

at Mirror.MessagePacking+<>c__DisplayClass6_0`2[T,C].b__0 (Mirror.NetworkConnection conn, Mirror.NetworkReader reader, System.Int32 channelId) [0x00096] in C:\Users\Kirill\SteamMultiplayerGame\Assets\Mirror\Runtime\MessagePacking.cs:119

UnityEngine.Debug:LogError (object)

Mirror.MessagePacking/<>c__DisplayClass6_0`2<Mirror.AddPlayerMessage, Mirror.NetworkConnection>:b__0 (Mirror.NetworkConnection,Mirror.NetworkReader,int) (at Assets/Mirror/Runtime/MessagePacking.cs:123)

Mirror.NetworkServer:UnpackAndInvoke (Mirror.NetworkConnectionToClient,Mirror.NetworkReader,int) (at Assets/Mirror/Runtime/NetworkServer.cs:443)

Mirror.NetworkServer:OnTransportData (int,System.ArraySegment`1,int) (at Assets/Mirror/Runtime/NetworkServer.cs:506)

Mirror.LocalConnectionToServer:Send (System.ArraySegment`1,int) (at Assets/Mirror/Runtime/LocalConnections.cs:88)

Mirror.NetworkConnection:Send<Mirror.AddPlayerMessage> (Mirror.AddPlayerMessage,int) (at Assets/Mirror/Runtime/NetworkConnection.cs:135)

Mirror.NetworkClient:AddPlayer () (at Assets/Mirror/Runtime/NetworkClient.cs:978)

Mirror.NetworkManager:OnClientConnect () (at Assets/Mirror/Runtime/NetworkManager.cs:1298)

Mirror.NetworkManager:OnClientConnect (Mirror.NetworkConnection) (at Assets/Mirror/Runtime/NetworkManager.cs:1304)

Mirror.NetworkManager:OnClientAuthenticated () (at Assets/Mirror/Runtime/NetworkManager.cs:1192)

Mirror.NetworkManager:OnClientConnectInternal () (at Assets/Mirror/Runtime/NetworkManager.cs:1174)

Mirror.LocalConnectionToServer:Update () (at Assets/Mirror/Runtime/LocalConnections.cs:102)

Mirror.NetworkClient:NetworkLateUpdate () (at Assets/Mirror/Runtime/NetworkClient.cs:1356)

Mirror.NetworkLoop:NetworkLateUpdate () (at Assets/Mirror/Runtime/NetworkLoop.cs:205)

did you ever find a solution?
i have the same problem