NullReferenceException is thrown on performing Undo and Redo actions when "Default Subgraph Operator" Template is opened, refer attached video

Steps to repro:
1. Create a new project
2. Windows > Package Manager > Visual Effects Graph > Install
3. Project > Packages > Visual Effect Graph > Editor > Templates > Open Default Subgraph Operator Template
4. Perform Undo (Ctrl + z) and Redo (Ctrl + y) actions for Window
5. On macOS Undo (cmd + z) and Redo (shift + cmd + z)

Actual Result:
NullReferenceException is throwing on Undo and Redo actions

Expected Result:
Actions can be performed without any exception thrown in the console

Reproducible in:
2020.1.0a6, 2019.3.0b5, 2019.3.0a10

Package Version found: 7.1.2, 7.1.1, 7.0.0.

NOTE:
Visual Effect Graph is introduced in 2019.3.0a10.

Environment:
Windows 10 & macOS 10.14

Stack Trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.VFX.VFXParameter.UpdateDefaultExpressionValue () (at Library/PackageCache/com.unity.visualeffectgraph@7.1.2/Editor/Models/Parameters/VFXParameter.cs:331)
UnityEditor.VFX.UI.VFXViewController.SynchronizeUndoRedoState () (at Library/PackageCache/com.unity.visualeffectgraph@7.1.2/Editor/GraphView/Views/Controller/VFXViewControllerUndo.cs:234)
UnityEditor.Undo.Internal_CallUndoRedoPerformed () (at <52c46852ed4749ed926125cda2005635>:0)
UnityEditor.EditorApplication:Internal_CallGlobalEventHandler()