How to reproduce:
1. Create a new Unity project using "High-Definition RP" template
2. Open Package Manager (Window/Package Manager)
3. Remove "HD Render Pipeline" package
4. Reinstall the same package version

Expected behavior: The lighting in the scene is the same as before removing the package.
Actual behavior: After reinstalling the package, the scene is grey (on some versions bluish or yellowish) and lots of ArgumentNullException errors are thrown in the Console window.

Reproducible with - 2018.2.0b7, 2018.2.0f2, 2018.2.6f1, 2018.3.0a10
Not reproducible with - 2018.1.9f2, 2018.2.0b6

Note: The same issue occurs with projects that are using Lightweight RP.

Errors that are thrown:
ArgumentNullException: Argument cannot be null.
Parameter name: value
UnityEngine.MaterialPropertyBlock.SetTexture (Int32 nameID, UnityEngine.Texture value) (at C:/buildslave/unity/build/Runtime/Export/Shader.cs:130)
<...>

Workaround: Reopening the project.