To reproduce:
1) open the project
2) click on CT_Part1_01_Fountains in the project tab
3) make sure the inspector tab shows the info for that asset and is visible
(if the tab is not visible in the layout this bug does not happen)
4) right click on CT_Part1_01_Fountains and select "reimport"
5) after the reimport click anywhere on the inspector tab (on the left of
the "revert" button of the model importer settings for example)
6) notice the errors:
MissingReferenceException: The object of type 'TestObject' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEditor.Editor.IsEnabled () (at C:/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:554)
UnityEditor.InspectorWindow.DrawEditor (UnityEditor.Editor editor, Int32 editorIndex, Boolean forceDirty, System.Boolean& showImportedObjectBarNext, UnityEngine.Rect& importedObjectBarRect, Boolean eyeDropperDirty) (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:1082)
UnityEditor.InspectorWindow.DrawEditors (UnityEditor.Editor[] editors) (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:969)
UnityEditor.InspectorWindow.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:350)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)