Steps to reproduce:

1. Create a project
2. Window->UI Toolkit->UI Builder
3. Go to the "Controls" window and find  the "Button"
4. Double-click on it
5. Verify, that button becomes added 
6. Select it
7. Verify, that its data becomes displayed in the "Inspector" window
8. Find the "Transition Animations" section 
9. Expand it;
10. Expand "Property" dropdown;
11. In the search field enter any letter and observe the "Console" view

 
Actual Result: Each time when a user enters some symbol, the console displays an error. Added screenshot and video in the "Attachments" section.

Expected Result: No errors in the Console view and the search should work.

Reproducible with: 2023.2.0a18 (FAV), 2023.2.0b11, 2023.3.0a7.

Not Reproducible with: 2021.3.30f1, 2022.3.10f1, 2023.1.11f1, 2023.2.0a17.

Error:

NullReferenceException: Object reference not set to an instance of an object
Unity.UI.Builder.CategoryDropdownField+WindowContent.OnSearchChanged (UnityEngine.UIElements.ChangeEvent`1[T] evt) (at /Users/bokken/build/output/unity/unity/Modules/UIBuilder/Editor/Utilities/CategoryDropdownField/CategoryDropdownField+WindowContent.cs:263)
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:228)
UnityEngine.UIElements.EventDispatchUtilities.HandleEventAcrossPropagationPath (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:183)
UnityEngine.UIElements.EventDispatchUtilities.DefaultDispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:564)
UnityEngine.UIElements.EventBase.Dispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventBase.cs:110)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:336)
UnityEngine.UIElements.EventDispatcher.ProcessEventQueue () (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:291)
UnityEngine.UIElements.EventDispatcher.OpenGate () (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:255)
UnityEngine.UIElements.EventDispatcherGate.Dispose () (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:78)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:346)
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:200)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Panel.cs:567)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:498)
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:225)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:74)
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:28)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:206)
h4.