If you have a C# script selected in Project View and the inspector is reloaded (either by recompiling or importing/refreshing the file), a NullReferenceException will occur.

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Experimental.AssetImporters.AssetImporterEditor.InternalSetTargets (UnityEngine.Object[] t) (at C:/buildslave/unity/build/Modules/AssetPipelineEditor/ImportSettings/AssetImporterEditor.cs:122)
UnityEditor.Editor.OnForceReloadInspector () (at C:/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:603)

1. Open Unity
2. Open the attached project
3. Find TestScript in the Project View and select it so the Inspector displays info about it
4. Right Click on the TestScript and Reimport
5. Right Click on the TestScript and Refresh

You can also see this happen by double clicking the TestScript in Project View to open it in a code editor, make changes and then return to the editor. The error will occur after recompiling.

Expected Result:
No errors appear in the console.

Actual Result:
A NullReferenceException occurs in the console.

Tested on Windows.

Reproduced on 2019.3.0a4

Cannot Reproduce on 2019.2.0b3, 2019.3.0a2, 2019.3.0a3