Unable to save VFX Subgraph Block along with NullReferenceException error on saving Empty Subgraph Block.

Steps to repro:
1. Create a new HDRP project.
2. Project Window > Click on "" > Visual Effects > Visual Effect Subgraph Block.
3. Open > Press Space bar > Type Empty Subgraph Block.
4. Click on Save.

Actual Result:
NullReferenceException error in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a20 with Package version 10.0.0-preview.27.

Working Fine in:
2020.2.0a20, 2020.1.2f1 with Package version 9.0.0-preview33.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stacktrace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.VFX.VisualEffectResourceExtensions.GetOrCreateGraph (UnityEditor.VFX.VisualEffectResource resource) (at library/packagecache/com.unity.visualeffectgraph@10.0.0-preview.27/editor/models/vfxgraph.cs:168)
UnityEditor.VFX.UI.VFXView.GetGraphsRecursively (UnityEditor.VFX.VFXGraph start, System.Collections.Generic.HashSet`1[T] graphs) (at library/packagecache/com.unity.visualeffectgraph@10.0.0-preview.27/editor/graphview/views/vfxview.cs:1194)
UnityEditor.VFX.UI.VFXView.OnSave () (at library/packagecache/com.unity.visualeffectgraph@10.0.0-preview.27/editor/graphview/views/vfxview.cs:1162)
UnityEngine.UIElements.Clickable.Invoke (UnityEngine.UIElements.EventBase evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.Clickable.ProcessUpEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.Vector2 localPosition, System.Int32 pointerId) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.Clickable.OnMouseUp (UnityEngine.UIElements.MouseUpEvent evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventCallbackFunctor`1[TEventType].Invoke (UnityEngine.UIElements.EventBase evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventCallbackRegistry.InvokeCallbacks (UnityEngine.UIElements.EventBase evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.CallbackEventHandler.HandleEvent (UnityEngine.UIElements.EventBase evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.CallbackEventHandler.HandleEventAtTargetPhase (UnityEngine.UIElements.EventBase evt) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.MouseCaptureDispatchingStrategy.DispatchEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.ApplyDispatchingStrategies (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel, System.Boolean imguiEventIsInitiallyUsed) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.ProcessEventQueue () (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.OpenGate () (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcherGate.Dispose () (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.UIElements.UIEventRegistration<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) (at <d683819026f84051943436699bfd6120>:0)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at <315b5ac1dd224a34a39e98ea4563da5e>:0)