Steps to reproduce:

1. Dock the UI Builder window (Window > UI Toolkit > UI Builder) in the same tab group as the Game window (the UI Builder window should not be visible when switched to Game window and vice versa)
2. Add a Label to the default document in UI Builder
3. Scroll to Text settings in the Inspector and expand
4. Switch the active tab to Game view so that UI Builder window wouldn't be visible
6. Go back to UI Builder
7. Click on any Text Align buttons without selecting or deselecting anything

Note: this will reproduce after switching to any tab as long as UI Builder loses focus

Expected result: no errors are thrown and proper references to the selected label item are rebuilt after switching back to the UI Builder window
Actual result: an error is thrown when changing Text Align settings

NullReferenceException: Object reference not set to an instance of an object
Unity.UI.Builder.BuilderCanvasStyleControls.HorizontalTextAlignUpdateToggleIcon () (at /Users/bokken/build/output/unity/unity/Modules/UIBuilder/Editor/Builder/Viewport/BuilderCanvasStyleControls.cs:330)

Reproducible with: 2021.1.0f1, 2022.2.0a1, 2023.1.0b5, 2023.2.0a3