Github: https://github.com/Unity-Technologies/InputSystem/issues/690

Repro:
1. Download attached project (with ISX and Quick Search package)
2. Drag "GameObject" into Project window to create a prefab
3. Observe the Console window
4. Try delete/duplicate/move the prefab to other folder, and observe the Console window.

Actual: When with both ISX and Quick Search package imported, changing a prefab file causes NullReferenceException.

Note: This does NOT happen when only Quick Search or ISX is installed. The bug only happens when both packages are present.

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.SettingsProvider.Repaint () (at C:/buildslave/unity/build/Editor/Mono/Settings/SettingsProvider.cs:123)
UnityEngine.InputSystem.Editor.InputSettingsProvider.ForceReload () (at Library/PackageCache/com.unity.inputsystem@0.2.10-preview/InputSystem/Editor/Settings/InputSettingsProvider.cs:351)
UnityEngine.InputSystem.InputSystem.OnProjectChange () (at Library/PackageCache/com.unity.inputsystem@0.2.10-preview/InputSystem/InputSystem.cs:1692)
UnityEditor.EditorApplication.Internal_CallProjectHasChanged () (at C:/buildslave/unity/build/Editor/Mono/EditorApplication.cs:242)
UnityEditorInternal.InternalEditorUtility:ProjectWindowDrag(HierarchyProperty, Boolean)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)