When despawning a client owned object, the client attempts to send a NetworkVariableDeltaMessage when the NetworkObject is "null"

[JayPeet]

Description

I have a situation where destroying a NetworkObject on the server causes the object to be deleted on the client while the clients NetworkBehaviourUpdater still tries to write its variables.
This results in the following callstack being spammed repeatedly

MissingReferenceException: The object of type 'MyNetworkBehaviour' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object. UnityEngine.Component.GetComponentInParent (System.Type t, System.Boolean includeInactive) (at <b5cd1660e28545eca6b51cc4a296a19e>:0) UnityEngine.Component.GetComponentInParent[T] () (at <b5cd1660e28545eca6b51cc4a296a19e>:0) Unity.Netcode.NetworkBehaviour.get_NetworkObject () (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkBehaviour.cs:326) Unity.Netcode.NetworkBehaviour.NetworkVariableUpdate (System.UInt64 targetClientId, System.Int32 behaviourIndex) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkBehaviour.cs:626) Unity.Netcode.NetworkBehaviour.VariableUpdate (System.UInt64 targetClientId) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkBehaviour.cs:598) Unity.Netcode.NetworkBehaviourUpdater.NetworkBehaviourUpdate (Unity.Netcode.NetworkManager networkManager) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkBehaviourUpdater.cs:61) Unity.Netcode.NetworkManager.OnNetworkManagerTick () (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkManager.cs:1604) Unity.Netcode.NetworkTickSystem.UpdateTick (System.Double localTimeSec, System.Double serverTimeSec) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Timing/NetworkTickSystem.cs:102) Unity.Netcode.NetworkManager.OnNetworkPreUpdate () (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkManager.cs:1568) Unity.Netcode.NetworkManager.NetworkUpdate (Unity.Netcode.NetworkUpdateStage updateStage) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkManager.cs:1476) Unity.Netcode.NetworkUpdateLoop.RunNetworkUpdateStage (Unity.Netcode.NetworkUpdateStage updateStage) (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkUpdateLoop.cs:185) Unity.Netcode.NetworkUpdateLoop+NetworkPreUpdate+<>c.<CreateLoopSystem>b__0_0 () (at Library/PackageCache/com.unity.netcode.gameobjects@aac7ffb9ef/Runtime/Core/NetworkUpdateLoop.cs:232)

Reproduce Steps

I attempted to create a test project but was unable to reproduce it outside of my project. I think it is to do with a client updating a network variable when the server destroys the NetworkObject

Actual Outcome

When the server despawns the NetworkObject, the client still tries to send changed NetworkVariableDeltaMessages even though the NetworkObject is null

Expected Outcome

If an object is Despawned, the client stops interacting with the NetworkObject.

Environment

• OS: Win 10
• Unity Version: 2022.2.0b4
• Netcode Version: latest
• Netcode Commit: [e.g. https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/commit/28109b4227a9a286682cb9c6f5852570d42e8642]

Additional Context

While trying to fix it myself, It seems that between NetworkBehaviourUpdater.AddForUpdate() and NetworkBehaviourUpdater.NetworkBehaviourUpdate() the NetworkObject becomes null

I have a "fix" in my branch which just makes sure to remove any null NetworkObject before running the update JayPeet@3c3b18a

[ashwinimurt]

Could you include an example that can reproduce this situation? That will help us narrow down.

[ashwinimurt]

Backlog: MTT-4459

[JayPeet]

I was unable to create a small repro project, however I am pretty certain its the same as this issue #2140 which was merged in recently.

Its something to do with a network object being despawned but the client still tries to write to its network variables

[ashwinimurt]

That is great! If you can confirm with the latest develop that contains the fix, we can close the ticket. Thank you!

[jeffreyrainy]

Would you be setup to run with code from the develop branch ? If so, I would expect the issue to be fixed after

#2143

Please let me know if that is not the case.

[JayPeet]

Yup that change did fix it, reverted my change on my local branch.

Appreciate it! :)