Null Reference Exception is thrown on creating Sprite Shape Profile asset in Project Panel.

Steps to Reproduce:
1. Create a new project.
2. Import attached "2D-spriteshape-master.zip" file into the project panel.
3. Create "SpriteShapeProfile" asset in Project Panel. Create >> Sprite Shape Profile >> Empty/Strip/Shape.

Note : "NullReferenceException" spamming the console window.

Reproduced On: 2018.1.0a5
Working fine On: 2017.3.0b10 , 2018.1.0a4
Regression On: 2018.1.0a5

Notes:
- Appears on both Mac and Windows
- Appears always

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.U2D.EditorGUIReflection.GetCurrentInspectorWindow () (at Assets/2d-spriteshape-Unity-2017.3-bc7b73caf0a872fa0a45a6532c16847536db60d7/Editor/EditorGUIReflection.cs:62)
UnityEditor.U2D.SpriteShapeEditor.OnInspectorGUI () (at Assets/2d-spriteshape-Unity-2017.3-bc7b73caf0a872fa0a45a6532c16847536db60d7/Editor/SpriteShapeEditor.cs:167)
UnityEditor.InspectorWindow.DrawEditor (UnityEditor.Editor[] editors, Int32 editorIndex, Boolean rebuildOptimizedGUIBlock, System.Boolean& showImportedObjectBarNext, UnityEngine.Rect& importedObjectBarRect) (at /Users/weswong/Work/unity1/unity/Editor/Mono/Inspector/InspectorWindow.cs:1245)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)