Steps to reproduce:
1. Create a project
2. Open UI Toolkit Layout Debugger (Window > UI Toolkit > Layout Debugger)
3. In Layout Debugger window press “Goto next complex update” button
4. Observe the Console window

Actual results: “NullReferenceException: Object reference not set to an instance of an object” error is thrown in the Console
Expected results: No errors are thrown in the Console

Reproducible with versions: 6000.0.45f1, 6000.1.0b12, 6000.2.0a8
Can’t test with versions: 2021.3.50f1, 2022.3.60f1 (UI Toolkit Layout Debugger window is not available)

Tested on (OS):  MacBook Pro Sequoia 15.3.2 (Apple M1 Max)
{code:java}
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.UIElements.Experimental.UILayoutDebugger.LayoutPanelDebuggerImpl.FindNextComplexUpdateLoop () (at /Users/bokken/build/output/unity/unity/Modules/UIElementsEditor/Debugger/LayoutDebugger/LayoutPanelDebuggerImpl.cs:234)
UnityEditor.UIElements.Experimental.UILayoutDebugger.LayoutPanelDebuggerImpl.<Initialize>b__47_4 () (at /Users/bokken/build/output/unity/unity/Modules/UIElementsEditor/Debugger/LayoutDebugger/LayoutPanelDebuggerImpl.cs:504)
UnityEngine.UIElements.Clickable.Invoke (UnityEngine.UIElements.EventBase evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:314)
UnityEngine.UIElements.Clickable.ProcessUpEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.Vector2 localPosition, System.Int32 pointerId) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:411)
UnityEngine.UIElements.Clickable.OnPointerUp (UnityEngine.UIElements.PointerUpEvent evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:278)
UnityEngine.UIElements.EventCallbackFunctor`1[TEventType].Invoke (UnityEngine.UIElements.EventBase evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventCallback.cs:64)
UnityEngine.UIElements.EventCallbackRegistry+DynamicCallbackList.Invoke (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventCallbackRegistry.cs:246)
UnityEngine.UIElements.EventDispatchUtilities.HandleEvent_BubbleUpCallbacks (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement element) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:384)
UnityEngine.UIElements.EventDispatchUtilities.HandleEventAcrossPropagationPathWithCompatibilityEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.EventBase compatibilityEvt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target, System.Boolean isCapturingTarget) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:313)
UnityEngine.UIElements.EventDispatchUtilities.PropagateEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target, System.Boolean isCapturingTarget) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:65)
UnityEngine.UIElements.EventDispatchUtilities.DispatchToCapturingElement (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:594)
UnityEngine.UIElements.EventDispatchUtilities.DispatchToCapturingElementOrElementUnderPointer (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:545)
UnityEngine.UIElements.PointerUpEvent.Dispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/PointerEvents.cs:1642)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:419)
UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:215)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Panel.cs:635)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:511)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:234)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:78)
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:32)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:224)
{code}