On assigning Material to None under Decal Projector component in the Inspector causes the editor to throw UnassignedReferenceException, Refer to the attached video.

Steps to repro:
1. Create a new HDRP project
2. Hierarchy > Create > Rendering > Decal Projector.
3. Inspector > Decal Projector > Material > None

Actual Result:
UnassignedReferenceException Material assigned set to None Decal Projector component in the Inspector

Expected Result:
No errors in the console.

Reproducible in:
2021.1.0a6, 2020.2.0b11, 2020.2.0b5, with package version 10.1.0, 10.0.0-preview.27

Working fine in:
2020.2.0b5, 2020.1.12f1 with Package Version 9.0.0-preview.71, 8.2.0, 8.1.0

Environment:
Occurring on Windows 10 & Mac 10.15.

Stack trace:
UnassignedReferenceException: The variable m_Material of DecalProjector has not been assigned.
You probably need to assign the m_Material variable of the DecalProjector script in the inspector.
UnityEngine.Rendering.HighDefinition.DecalSystem.IsDecalMaterial (UnityEngine.Material material) (at library/packagecache/com.unity.render-pipelines.high-definition@10.1.0/runtime/material/decal/decalsystem.cs:369)
UnityEditor.Rendering.HighDefinition.DecalProjectorEditor.OnInspectorGUI () (at library/packagecache/com.unity.render-pipelines.high-definition@10.1.0/editor/material/decal/decalprojectoreditor.cs:425)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <e020ad89c1af43769f98694c4076cf19>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)