NullReferenceException in NetworkTrafficStatistics with Debug Inspector

[korzewarrior]

NullReferenceException in NetworkTrafficStatistics with Debug Inspector

Environment

• Unity Version: 6.3 LTS
• Fish-Networking Version: 4.6.18
• Platform: Windows 11

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Troubleshooting Steps Already Taken

1. Verified NetworkTrafficStatistics.EnableMode is set to Disabled on the StatisticsManager
2. Confirmed the issue only occurs when Inspector is in Debug mode
3. Traced the stack to identify the null reference location
4. Identified that _serverTraffic / _clientTraffic are null when accessed

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Description

When the Unity Inspector is switched to Debug mode and a NetworkObject with prediction ([Replicate]/[Reconcile] methods) is selected in the Hierarchy, a NullReferenceException is thrown repeatedly in NetworkTrafficStatistics.AddInboundPacketIdData().

The error occurs every network tick, flooding the console and breaking gameplay until Play mode is stopped. This happens even when NetworkTrafficStatistics.EnableMode is set to Disabled.

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Replication Steps

1. Open a project with FishNet 4.6.18
2. Create or use any NetworkBehaviour with [Replicate] and [Reconcile] prediction methods (FishNet's prediction samples would work)
3. Enter Play mode as Host (server + client)
4. Spawn the predicted NetworkObject
5. In the Inspector window, click the three-dot menu (⋮) in the top-right
6. Select "Debug" to switch to Debug Inspector mode
7. Click on the spawned NetworkObject in the Hierarchy
8. Observe the NullReferenceException spam in the Console

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Expected Behavior

Selecting a NetworkObject in Debug Inspector mode should not cause errors. The statistics tracking code should gracefully handle cases where internal traffic objects are not initialized.

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Actual Behavior

The following exception is thrown every tick:

NullReferenceException: Object reference not set to an instance of an object
FishNet.Managing.Statistic.NetworkTrafficStatistics.AddInboundPacketIdData (FishNet.Transporting.PacketId typeSource, System.String details, System.Int32 bytes, UnityEngine.GameObject gameObject, System.Boolean asServer) (at Assets/FishNet/Runtime/Managing/Statistic/NetworkTrafficStatistics.cs:208)
FishNet.Object.NetworkBehaviour.Server_SendReconcileRpc[T] (System.UInt32 hash, T& lastReconcileData, T reconcileData, FishNet.Transporting.Channel channel) (at Assets/FishNet/Runtime/Object/NetworkBehaviour/NetworkBehaviour.Prediction.cs:458)
FishNet.Object.NetworkBehaviour.Reconcile_Server[T] (System.UInt32 methodHash, T& lastReconcileData, T data, FishNet.Transporting.Channel channel) (at Assets/FishNet/Runtime/Object/NetworkBehaviour/NetworkBehaviour.Prediction.cs:1287)
FishNet.Object.NetworkBehaviour.Reconcile_Current[T] (System.UInt32 hash, T& lastReconcileData, GameKit.Dependencies.Utilities.Types.RingBuffer`1[T] reconcilesHistory, T data, FishNet.Transporting.Channel channel) (at Assets/FishNet/Runtime/Object/NetworkBehaviour/NetworkBehaviour.Prediction.cs:1342)
PawnPrediction.PerformReconcile (PawnPrediction+ReconcileData rd, FishNet.Transporting.Channel channel) (at <generated>:0)
PawnPrediction.CreateReconcile () (at Assets/_Starboys/Scripts/Pawn/PawnPrediction.cs:319)
PawnPrediction.TimeManager_OnTick () (at Assets/_Starboys/Scripts/Pawn/PawnPrediction.cs:312)
FishNet.Managing.Timing.TimeManager.IncreaseTick () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:738)
FishNet.Managing.Timing.TimeManager.<TickUpdate>g__MethodLogic|113_0 () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:389)
FishNet.Managing.Timing.TimeManager.TickUpdate () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:377)
FishNet.Transporting.NetworkReaderLoop.Update () (at Assets/FishNet/Runtime/Transporting/NetworkReaderLoop.cs:29)

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Root Cause Analysis

In NetworkTrafficStatistics.cs, the method AddInboundPacketIdData() (line 208) calls:

GetBidirectionalNetworkTraffic(asServer).InboundTraffic.AddPacketIdData(...)

Where GetBidirectionalNetworkTraffic() returns:

private BidirectionalNetworkTraffic GetBidirectionalNetworkTraffic(bool asServer) 
    => asServer ? _serverTraffic : _clientTraffic;

The fields _serverTraffic and _clientTraffic are only initialized in InitializeOnce_Internal(). When Unity's Debug Inspector uses reflection to serialize/access fields on the NetworkBehaviour, it can trigger the reconcile code path in a context where these traffic objects are null.

The existing null check in NetworkBehaviour.Prediction.cs:455:

if (_networkTrafficStatistics != null)

...passes because the NetworkTrafficStatistics object exists, but its internal _serverTraffic/_clientTraffic fields are null.

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Suggested Fix

Add null guards in NetworkTrafficStatistics.cs before accessing traffic objects:

internal void AddInboundPacketIdData(PacketId typeSource, string details, int bytes, GameObject gameObject, bool asServer)
{
    if (bytes <= 0)
        return;

    var traffic = GetBidirectionalNetworkTraffic(asServer);
    if (traffic == null || traffic.InboundTraffic == null)
        return;

    traffic.InboundTraffic.AddPacketIdData(typeSource, details, (ulong)bytes, gameObject);
}

Apply the same pattern to:

• AddOutboundPacketIdData()
• AddInboundSocketData()
• AddOutboundSocketData()

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Additional Notes

• Switching the Inspector back to Normal mode stops the errors, but gameplay may already be broken
• This occurs even with StatisticsManager.NetworkTraffic.EnableMode set to Disabled
• The issue appears to be an Editor-only problem triggered by reflection-based field access

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Contact Discord: korzewarrior

[FirstGearGames]

Another user indicates this may be an issue even in 4.6.20. The issue has been re-opened but a project to reproduce the issue must still be supplied.

[ninjuit]

Reproduction Project: FishNet_ExampleProject.zip

Version: Unity 6000.3.4f1
Fish-Networking: Version 4.6.20R
Platform: Windows 11

Description / Notes:
This is a brand new unity project where I have done nothing but:
-Import the 4.6.20R package
-Drag the NetworkManager prefab from Demos into the SampleScene.
-Run the game
-Click Server then Client

Simple Reproduction Steps:
-Download and open the repo project, FishNet_ExampleProject
-Open SampleScene
-Make sure that you have 2 inspectors tabs/windows open. One should be set to Debug mode. (It's possible you only need the one debug inspector, but telling you how I had it set up)
-Before pressing Play, click the NetworkManager so that it is the inspected object
-Press Play to start the game
-Click Server
-Click Client
-Error is thrown continuously:

NullReferenceException: Object reference not set to an instance of an object FishNet.Managing.Statistic.NetworkTrafficStatistics.AddOutboundSocketData (System.UInt64 bytes, System.Boolean asServer) (at Assets/FishNet/Runtime/Managing/Statistic/NetworkTrafficStatistics.cs:197) FishNet.Managing.Transporting.TransportManager.<IterateOutgoing>g__SendAsClient|69_1 (FishNet.Managing.Transporting.TransportManager+<>c__DisplayClass69_0& ) (at Assets/FishNet/Runtime/Managing/Transporting/TransportManager.cs:900) FishNet.Managing.Transporting.TransportManager.IterateOutgoing (System.Boolean asServer) (at Assets/FishNet/Runtime/Managing/Transporting/TransportManager.cs:772) FishNet.Managing.Timing.TimeManager.TryIterateData (System.Boolean incoming) (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:1117) FishNet.Managing.Timing.TimeManager.IncreaseTick () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:766) FishNet.Managing.Timing.TimeManager.<TickUpdate>g__MethodLogic|113_0 () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:392) FishNet.Managing.Timing.TimeManager.TickUpdate () (at Assets/FishNet/Runtime/Managing/Timing/TimeManager.cs:380) FishNet.Transporting.NetworkReaderLoop.Update () (at Assets/FishNet/Runtime/Transporting/NetworkReaderLoop.cs:29)