Description

Setting a ParticleSystem component in a Blueprint to none/null with a "Set Template" node causes the editor and the packaged project to crash. I have noticed this when migrating my game to 4.22, which makes use of variables to set and unset particle effects on certain actors. This is a regression from 4.21.2 (CL-4753647).

This was reported and tested in 4.22 (CL-5660361). This was reproduced in Main 4.23 (CL-5745677).

Steps to Reproduce
  1. Open the UE4 Editor and create a Blank project
  2. Create an Actor Blueprint with a ParticleSystem component
  3. Create an event or function that toggles the ParticleSystem component, via a "Set Template" node, between a real particle system template and a "none" (null) one
  4. Call this function/event however you wish. For example, with a Set Timer node
  5. Add the Actor to the level and Play-in-Editor

Results: The editor crashes when previewed in-editor. The packaged game crashes with a "Fatal error!"

Expected: The project does not crash

Callstack
[2019.04.04-18.56.28:145][206]LogWindows: Error: === Critical error: ===
[2019.04.04-18.56.28:145][206]LogWindows: Error: 
[2019.04.04-18.56.28:145][206]LogWindows: Error: Fatal error!
[2019.04.04-18.56.28:145][206]LogWindows: Error: 
[2019.04.04-18.56.28:145][206]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x000001ac
[2019.04.04-18.56.28:145][206]LogWindows: Error: 
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5d959079 UE4Editor-Engine.dll!UParticleSystemComponent::CanSkipTickDueToVisibility() [d:\builds-main\engine\source\runtime\engine\private\particles\particlecomponents.cpp:3511]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5d9f581a UE4Editor-Engine.dll!FParticleSystemWorldManager::ProcessTickList<0>() [d:\builds-main\engine\source\runtime\engine\private\particles\particlesystemmanager.cpp:539]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5da43ed7 UE4Editor-Engine.dll!FParticleSystemWorldManager::Tick() [d:\builds-main\engine\source\runtime\engine\private\particles\particlesystemmanager.cpp:656]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5da0b701 UE4Editor-Engine.dll!FParticleSystemWorldManagerTickFunction::ExecuteTick() [d:\builds-main\engine\source\runtime\engine\private\particles\particlesystemmanager.cpp:757]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5decb7cd UE4Editor-Engine.dll!TGraphTask<FTickFunctionTask>::ExecuteTask() [d:\builds-main\engine\source\runtime\core\public\async\taskgraphinterfaces.h:847]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc618a1e17 UE4Editor-Core.dll!FNamedTaskThread::ProcessTasksNamedThread() [d:\builds-main\engine\source\runtime\core\private\async\taskgraph.cpp:685]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc618a20d3 UE4Editor-Core.dll!FNamedTaskThread::ProcessTasksUntilQuit() [d:\builds-main\engine\source\runtime\core\private\async\taskgraph.cpp:582]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc618b1ff9 UE4Editor-Core.dll!FTaskGraphImplementation::WaitUntilTasksComplete() [d:\builds-main\engine\source\runtime\core\private\async\taskgraph.cpp:1457]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5dee6cff UE4Editor-Engine.dll!FTickTaskSequencer::ReleaseTickGroup() [d:\builds-main\engine\source\runtime\engine\private\ticktaskmanager.cpp:557]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5deebc82 UE4Editor-Engine.dll!FTickTaskManager::RunTickGroup() [d:\builds-main\engine\source\runtime\engine\private\ticktaskmanager.cpp:1505]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5d7457ff UE4Editor-Engine.dll!UWorld::RunTickGroup() [d:\builds-main\engine\source\runtime\engine\private\leveltick.cpp:789]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5d75001f UE4Editor-Engine.dll!UWorld::Tick() [d:\builds-main\engine\source\runtime\engine\private\leveltick.cpp:1576]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5ba63aad UE4Editor-UnrealEd.dll!UEditorEngine::Tick() [d:\builds-main\engine\source\editor\unrealed\private\editorengine.cpp:1618]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffc5c28a1f6 UE4Editor-UnrealEd.dll!UUnrealEdEngine::Tick() [d:\builds-main\engine\source\editor\unrealed\private\unrealedengine.cpp:403]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ff7c66471a6 UE4Editor.exe!FEngineLoop::Tick() [d:\builds-main\engine\source\runtime\launch\private\launchengineloop.cpp:4043]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ff7c665672c UE4Editor.exe!GuardedMain() [d:\builds-main\engine\source\runtime\launch\private\launch.cpp:173]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ff7c66567aa UE4Editor.exe!GuardedMainWrapper() [d:\builds-main\engine\source\runtime\launch\private\windows\launchwindows.cpp:145]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ff7c6664afc UE4Editor.exe!WinMain() [d:\builds-main\engine\source\runtime\launch\private\windows\launchwindows.cpp:275]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ff7c666760e UE4Editor.exe!__scrt_common_main_seh() [d:\agent\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffcd5211fe4 KERNEL32.DLL!UnknownFunction []
[2019.04.04-18.56.28:145][206]LogWindows: Error: [Callstack] 0x00007ffcd75fcb81 ntdll.dll!UnknownFunction []

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Fixed
ComponentRendering - Cascade
Affects Versions4.224.23
Target Fix4.22.1
Fix Commit5809030
Main Commit5809073
CreatedApr 4, 2019
ResolvedApr 9, 2019
UpdatedApr 24, 2019