NullReferenceException error is thrown on removing Decal Projector component.

Steps to repro:
1. Create a new HDRP Project.
2. Hierarchy > Right Click > Rendering > Decal Project.
3. Inspector > Remove Decal ProjectComponent.

Actual Result:
NullReferenceException error is thrown in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a10, 2020.1.0b8, 2019.3.0f3 with Package Version: 9.0.0, 8.1.0, 8.0.1, 7.1.8.

Environment:
Occurring on Windows 10 & Mac 10.15

Stack trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Rendering.HighDefinition.DecalProjectorEditor.OnDisable () (at library/packagecache/com.unity.render-pipelines.high-definition@8.1.0/editor/material/decal/decalprojectoreditor.cs:130)