How to reproduce:

1. Create a new graph and add it to the scene
2. Add custom HLSL block to Update context
3. Save graph

Observe that vfx is no longer rendered and error is thrown to the console

Note: couldn't repro on 2023.3.0a3

Unity cannot compile the VisualEffectAsset at path "Assets/TEST hlsl/Main Graph.vfx" because of the following exception:
UnityEngine.UnassignedReferenceException: The variable m_ShaderFile of CustomHLSL has not been assigned.
You probably need to assign the m_ShaderFile variable of the CustomHLSL script in the inspector. at UnityEngine.Object+MarshalledUnityObject.TryThrowEditorNullExceptionObject