Material has an invalid configuration error is thrown on assigning Texture to none in the exposed Properties section.

Steps to repro:
1. Open the attached project.
2. Open Test scene > Hierarchy > Capsule Game object.
3. Inspector > Expand Shader2 material > Exposed Properties.
4. Test1 > Assign to None.

Actual Result:
Material has an invalid configuration error is thrown on assigning Texture to none

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a18, 2020.1.0f1, 2020.1.0b13 with Package version 9.0.0 preview.33

Note: Graph Inspector introduced in Package version 9.0.0 preview.33.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stacktrace:
Error in Material 'Shader2': 'Texture Stack 2 (NULL, ConstructionLight_MetallicOcculusionSmoothness)' has an invalid configuration
Texture Stack incomplete: no texture at layer 1
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)