MissingReferenceException thrown on clicking on "Save Asset" after creating SubGraph and saving it without having any changes

Steps to Reproduce:

1. Create a new Project with HDRP Template
2. Install Package Manager > HDRP package > 7.2.0
3. Install Package Manager > Shader Graph > 7.2.0
4. Create Assets > right-click > Shader > PBR Graph
5. Create new node from New Shader Graph window > PBR Master > Vertex Position > Artistic > Adjustment > Channel Mixer
6. Select Shader Graph window > Channel Mixer > right-click > Convert To SubGraph
7. Double Click on Project > Assets > New Shader Sub Graph > New Shader Sub Graph window > Save Assets

Expected Result:
Sub Graph is saved

Actual Result:
"MissingReferenceException: The object of type 'SubGraphAsset' has been destroyed but you are still trying to access it" is thrown

Reproducible on: 2020.1.0a23, 2020.1.0a1, 2019.3.3f1, 2019.3.2f1, 2019.3.0a7

Reproducible Package version: 7.2.1, 7.2.0, 7.1.8, 7.1.5, 7.1.1

Working fine in:
2020.1.0a24 with package Version 7.2.1
2019.3.0a6 with Package Version 6.9.2.

Environment: Windows 10 and Mac 10.14

Stack Trace

MissingReferenceException: The object of type 'SubGraphAsset' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Object.get_name () (at <94c5f4c38cdc42d2b006f8badef04394>:0)
UnityEditor.Editor.get_targetTitle () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.Experimental.AssetImporters.AssetImporterEditor.get_targetTitle () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.Experimental.AssetImporters.ScriptedImporterEditor.get_targetTitle () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.Editor.OnHeaderGUI () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.Editor.DrawHeader () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.UIElements.EditorElement.DrawEditorLargeHeader (UnityEditor.Editor[] editors, System.Boolean& wasVisible) (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.UIElements.EditorElement.DrawEditorHeader (UnityEditor.Editor[] editors, UnityEngine.Object target, System.Boolean& wasVisible) (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEditor.UIElements.EditorElement.HeaderOnGUI () (at <9ba1187881a84a08b5f9c4cb333d7a6a>:0)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Boolean canAffectFocus) (at <57fa7f4ad1c34ed185465e0a9f71c244>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)