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Steps to reproduce:
1. Create new Unity project using Universal 3D Template
2. Open UI Library window (right-click in Hierarchy > UI Toolkit > Standard Elements > UI Library)
3. In UI Library find “Animation Play State Style Enum Field ” and double click on it to create it
4. In “Open UI stage” pop-up press “Continue” and save UXML file
5. Once the files are created, observe the Console window
Actual results: “NullReferenceException: Object reference not set to an instance of an object” errors are thrown in the Console window
Expected results: No errors are thrown in the Console window
Reproducible with versions: 6000.6.0a7
Can’t test with versions: 6000.6.0a6 and lower (No such feature to create UI Elements in Hierarchy window)
Tested on (OS): macOS Tahoe 26.4.1 (M1)
NullReferenceException: Object reference not set to an instance of an object Unity.UIToolkit.Editor.LiveAttributePropertyController.CollectLiveAttributeValuePropertyModifications (System.Object obj, System.Object uxmlSerializedData, UnityEditor.UIElements.UxmlSerializedAttributeDescription attributeDescription, UnityEditor.SerializedProperty property, System.Collections.Generic.List`1[T] propertyModifications, System.Boolean& hasUnsupportedDrivenPropertyChange, System.Boolean syncOnlyBoundValues, System.Collections.Generic.HashSet`1[T] resolvedBindingLookup) (at /Users/bokken/build/output/unity/unity/Modules/UIToolkitAuthoringEditor/Managed/Inspector/Controls/LiveAttributePropertyController.cs:173) Rethrow as Exception: Failed to collect modifications validation UnityEngine.Debug:LogException(Exception) Unity.UIToolkit.Editor.LiveAttributePropertyController:CollectLiveAttributeValuePropertyModifications(Object, Object, UxmlSerializedAttributeDescription, SerializedProperty, List`1, Boolean&, Boolean, HashSet`1) (at /Users/bokken/build/output/unity/unity/Modules/UIToolkitAuthoringEditor/Managed/Inspector/Controls/LiveAttributePropertyController.cs:338)
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