Add the following script to a new project

```

using UnityEngine.UIElements;

[UxmlElement]
public partial class Example : VisualElement
{
    [UxmlObjectReference]
    public object someValue;
}

```

Examine the editor log, the following error will be found:

 
warning CS8785: Generator 'UxmlSerializedDataGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'NullReferenceException' with message 'Object reference not set to an instance of an object.'
[689/696    0s] ILPostProcess Library/Bee/artifacts/1900b0aEDbg.dag/post-processed/Assembly-CSharp.dll (+pdb)