On adding Texture in "Density Mask Texture" under the "Density Volume" component, the editor threw in the console

Steps to repro:
1. Create a new HDRP template project.
2. Hierarchy > right-click > Rendering > Density Volume
3. Inspector > Density Volume > Density Mask Texture > Texture > Add Texture

Actual Result:
NullReferenceException is thrown on adding Texture in "Density Mask Texture" under the "Density Volume" component

Expected Result:
No errors in the console.

Reproducible in:
2021.1.0a5, 2021.1.0a4 with Package Version 10.1.0.
2021.1.0a1 with Package Version 8.1.0

Working Fine in:
2020.2.0b11 with Package Version 10.1.0.

Note: Package Version 10.1.0 is not available in 2021.1.0a3 to 2021.1.0a1.

Environment:
Occurring on Windows 10 & mac 10.15.