[AI] Destroying an actor while using pooled actors with MassActorSpawnerSubsystem causes a nullptr exception crash

If an actor that is used in the pooled actor list of UMassActorSpawnerSubsystem is destroyed, it causes a nullptr exception in UMassActorSpawnerSubsystem::SpawnOrRetrieveFromPool. The subsystem attempts to use the first entry of its pooled actors list without checking for a nullptr.

Additionally, this can cause a crash when ReleaseActorToPool is called if the entity that is detached is invalid. The check that is triggered is in UMassRepresentationSubsystem::OnMassAgentComponentEntityDetaching.

1. Open MassCrowd level in CitySample
2. In World Settings, set the Kill Z to -5.0
3. Open BP_CrowdCharacter and change the function Can Be Pooled to return true
4. PIE
5. Delete the Floor from the level
6. After some of the AI hit the Kill Z and are GC'd
7. In BP_MassCrowdSpawner actor in the level press DEBUG_Spawn or DEBUG_Clear

UnrealEditor_MassActors!UMassActorSpawnerSubsystem::SpawnOrRetrieveFromPool() [D:\UE_5.1\Engine\Plugins\Runtime\MassGameplay\Source\MassActors\Private\MassActorSpawnerSubsystem.cpp:195]
UnrealEditor_MassActors!UMassActorSpawnerSubsystem::ProcessPendingSpawningRequest() [D:\UE_5.1\Engine\Plugins\Runtime\MassGameplay\Source\MassActors\Private\MassActorSpawnerSubsystem.cpp:282]
UnrealEditor_MassActors!UMassActorSpawnerSubsystem::OnPrePhysicsPhaseStarted() [D:\UE_5.1\Engine\Plugins\Runtime\MassGameplay\Source\MassActors\Private\MassActorSpawnerSubsystem.cpp:380]
UnrealEditor_MassActors!TBaseUObjectMethodDelegateInstance<0,UMassActorSpawnerSubsystem,void __cdecl(float),FDefaultDelegateUserPolicy>::ExecuteIfSafe() [D:\UE_5.1\Engine\Source\Runtime\Core\Public\Delegates\DelegateInstancesImpl.h:618]
UnrealEditor_MassEntity!TMulticastDelegate<void __cdecl(float),FDefaultDelegateUserPolicy>::Broadcast() [D:\UE_5.1\Engine\Source\Runtime\Core\Public\Delegates\DelegateSignatureImpl.inl:975]
UnrealEditor_MassEntity!FMassProcessingPhase::ExecuteTick() [D:\UE_5.1\Engine\Plugins\Runtime\MassEntity\Source\MassEntity\Private\MassProcessingPhaseManager.cpp:66]
UnrealEditor_Engine!FTickFunctionTask::DoTask() [D:\UE_5.1\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:284]
UnrealEditor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() [D:\UE_5.1\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:1348]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksNamedThread() [D:\UE_5.1\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:760]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [D:\UE_5.1\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:649]
UnrealEditor_Core!FTaskGraphCompatibilityImplementation::WaitUntilTasksComplete() [D:\UE_5.1\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:2203]
UnrealEditor_Engine!FTickTaskSequencer::ReleaseTickGroup() [D:\UE_5.1\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:565]
UnrealEditor_Engine!FTickTaskManager::RunTickGroup() [D:\UE_5.1\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:1592]
UnrealEditor_Engine!UWorld::RunTickGroup() [D:\UE_5.1\Engine\Source\Runtime\Engine\Private\LevelTick.cpp:794]
UnrealEditor_Engine!UWorld::Tick() [D:\UE_5.1\Engine\Source\Runtime\Engine\Private\LevelTick.cpp:1537]
UnrealEditor_UnrealEd!UEditorEngine::Tick() [D:\UE_5.1\Engine\Source\Editor\UnrealEd\Private\EditorEngine.cpp:1890]
UnrealEditor_UnrealEd!UUnrealEdEngine::Tick() [D:\UE_5.1\Engine\Source\Editor\UnrealEd\Private\UnrealEdEngine.cpp:517]
UnrealEditor!FEngineLoop::Tick() [D:\UE_5.1\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp:5369]
UnrealEditor!GuardedMain() [D:\UE_5.1\Engine\Source\Runtime\Launch\Private\Launch.cpp:202]
UnrealEditor!GuardedMainWrapper() [D:\UE_5.1\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:107]
UnrealEditor!LaunchWindowsStartup() [D:\UE_5.1\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:244]
UnrealEditor!WinMain() [D:\UE_5.1\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:282]
UnrealEditor!__scrt_common_main_seh() [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
kernel32

I am not able to find world outliner how to enable it?

Bonjour j'ai un petit problème c'est que je ne vois plus l'onglet "scability" pour changer les graphismes de uefn et j'ai pas trouvé l'option pour le faire revenir ?

How to achieve HLSL Multiple Render Target in Material blueprints?

How can i modify the param name in EQS node

Undefined sysmbol: typeinfo for AActor when cross-compile linux dedicated server on windows

How does TextureRenderTarget2D get TArray<uint8> type data?

How does UMG set overlapping layouts?

When I open UE4 4.24.3 it appears that. Does anyone know how to solve?

Why does the system plugin 'UnrealBuildTool' error could not be found when the project is compiled?

What method is used to fill polygonal regions when drawing spline mesh at run time?