*Steps to reproduce:*

Disclaimer! It will need lots of patience

1. Import the attached package

2. Perform around 20-30 clipboard operations, here are some suggestions that will likely to reproduce the issue:

2.1 Removing StripRatio from blackboard, Init context, changing location in graph of Get Strip Ratio and then deleting  (attached video of reproduction) (other graph elements can be used as well)

3. Then continuously press CMD + Z or CTRL + Z

*Actual results:* Occasionally, the application crashes or throws errors when using the undo or redo actions, especially if the keyboard shortcut is pressed repeatedly without releasing the key. Errror messages also happens during regular actions, like moving an operator to a different location in the graph.

*Expected results:* no crash or editor freeze, no errors are thrown in upon undo and redo operations

*Reproducible with versions:* 2022.3.48f1 (Editor freeze, and when quitting an application it finally crashes), 6000.0.22f1

*Not reproducible with versions:* n/a

*Can’t test with versions:* n/a

*Tested on (OS):* 

*Notes:*

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.VFX.UI.VFXGraphUndoStack.RestoreState () (at ./Library/PackageCache/com.unity.visualeffectgraph/Editor/GraphView/Views/Controller/VFXViewControllerUndo.cs:168)
UnityEditor.VFX.UI.VFXViewController.SynchronizeUndoRedoState () (at ./Library/PackageCache/com.unity.visualeffectgraph/Editor/GraphView/Views/Controller/VFXViewControllerUndo.cs:326)
UnityEditor.Undo.Internal_CallUndoRedoPerformed () (at /Users/bokken/build/output/unity/unity/Editor/Mono/Undo/Undo.bindings.cs:330)
UnityEditor.EditorApplication:Internal_CallGlobalEventHandler() (at /Users/bokken/build/output/unity/unity/Editor/Mono/EditorApplication.cs:520)

NullReferenceException: VFXMemorySerializer::StoreObject failure.
UnityEditor.VFX.VFXMemorySerializer.StoreObjectsToByteArray (UnityEngine.ScriptableObject[] objects, UnityEngine.CompressionLevel compressionLevel) (at <030039febc8b491cae744df4e5e7a370>:0)
UnityEditor.VFX.VFXGraph.Backup () (at ./Library/PackageCache/com.unity.visualeffectgraph/Editor/Models/VFXGraph.cs:829)
UnityEditor.VFX.UI.VFXGraphUndoStack.FlushState () (at ./Library/PackageCache/com.unity.visualeffectgraph/Editor/GraphView/Views/Controller/VFXViewControllerUndo.cs:125)
UnityEditor.VFX.UI.VFXViewController.WillFlushUndoRecord () (at ./Library/PackageCache/com.unity.visualeffectgraph/Editor/GraphView/Views/Controller/VFXViewControllerUndo.cs:313)
UnityEditor.Undo.Internal_CallWillFlushUndoRecord () (at /Users/bokken/build/output/unity/unity/Editor/Mono/Undo/Undo.bindings.cs:322)

Notes:
* After several repros, I couldn't find any meaningful callstack in Editor.log
* After 2-3 minutes timeframe of trying I reproduced the issue 2 times on 22.3.48f1 and 2 times on 6000.0.22f1