If you have Debug view turned on in the Inspector with an asmdef file selected and then de-select it, an error will appear in the console:

AssemblyDefinitionImporterInspector.OnInspectorGUI must call ApplyRevertGUI to avoid unexpected behaviour.
UnityEditor.Experimental.AssetImporters.AssetImporterEditor:OnDisable()

1. Open Unity
2. Open the attached project
3. Ensure that the Debug view is turned on in the Inspector
4. In Project View, select TestAssembly.asmdef
5. In Project View, select a different file or folder

Expected Result:
The asmdef file is deselected and no errors appear in the console.

Actual Result:
An error appears in the console.

Tested on Windows.

Reproduced on 2019.2.0a6, 2019.2.0b4, 2019.3.0a4, 2019.4.0f1

Cannot Reproduce on 2019.1.3f1, 2018.4.0f1, 2019.2.0a5