GraphPointerException occurs when assigned graph/state asset is deleted and graph property is clicked on State/Graph machine component

Steps to repro:
1. Create a new Project
2. Project window > Right-click > Create > Visual Scripting > Script
3. Hierarchy > right-click > create empty
4. Hierarchy > select GameObject > Add Component > Script Machine
5. Drag and drop and attach Script Graph to Script Machine
6. Delete Script graph asset from the project window
7. Hierarchy > select GameObject > Click on Missing Graph property on the inspector

Actual Result:
GraphPointerException appears on the console window

Expected Result:
No error appears in the console or a warning appears in the console telling the graph is missing

Reproducible on: 2021.2.0a4, 2021.1.0b5, 2021.1.0b1

Note: Visual Scripting was introduced in 2021.1.0b1

Package Version 1.5.1-pre.3

Environment:
Windows 10, Mac 10.15

Stack Trace:
GraphPointerException: Graph pointer is invalid.
[ GameObject ]
Unity.VisualScripting.GraphPointer.EnsureValid () (at Library/PackageCache/com.unity.visualscripting@1.5.1-pre.3/Runtime/VisualScripting.Core/Graphs/GraphPointer.cs:587)
Unity.VisualScripting.GraphWindow.set_reference (Unity.VisualScripting.GraphReference value) (at Library/PackageCache/com.unity.visualscripting@1.5.1-pre.3/Editor/VisualScripting.Core/Windows/GraphWindow.cs:77)
Unity.VisualScripting.GraphWindow.MatchSelection () (at Library/PackageCache/com.unity.visualscripting@1.5.1-pre.3/Editor/VisualScripting.Core/Windows/GraphWindow.cs:161)
Unity.VisualScripting.GraphWindow._OnProjectChange () (at Library/PackageCache/com.unity.visualscripting@1.5.1-pre.3/Editor/VisualScripting.Core/Windows/GraphWindow.cs:254)
Unity.VisualScripting.EditorApplicationUtility.OnProjectChange () (at Library/PackageCache/com.unity.visualscripting@1.5.1-pre.3/Editor/VisualScripting.Core/Utilities/EditorApplicationUtility.cs:144)
UnityEditor.EditorApplication.Internal_CallProjectHasChanged () (at <d7ddb8158a2944f3808fbb0703d4e132>:0)