FileNotFoundException error is thrown on closing Shader Graph window after deleting the shader.

Steps to repro:
1. Create a new Project with HDRP template.
2. Project Window > Right Click > Create > Shader > PBR graph.
3. Open the Newly Created Graph > Delete the Graph from Project Window.
4. Close Shader Graph Window.

Actual Result:
FileNotFoundException error is thrown in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a5, 2020.1.0b4, 2020.1.0b1, 2020.1.0a23 with Package Version 8.0.1.

Working Fine:
2020.2.0a5 with Package Version 7.3.1, 7.1.7
2019.3.8f1 with Package Version 7.3.1.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stack trace:
FileNotFoundException: Could not find file "E:\MyP4Final\New Unity Project\Assets\New Shader Graph.shadergraph"
System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.Boolean anonymous, System.IO.FileOptions options) (at <437ba245d8404784b9fbab9b439ac908>:0)
System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.IO.FileOptions options, System.String msgPath, System.Boolean bFromProxy, System.Boolean useLongPath, System.Boolean checkHost) (at <437ba245d8404784b9fbab9b439ac908>:0)
(wrapper remoting-invoke-with-check) System.IO.FileStream..ctor(string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,int,System.IO.FileOptions,string,bool,bool,bool)
System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, System.Boolean detectEncodingFromByteOrderMarks, System.Int32 bufferSize, System.Boolean checkHost) (at <437ba245d8404784b9fbab9b439ac908>:0)
System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, System.Boolean detectEncodingFromByteOrderMarks, System.Int32 bufferSize) (at <437ba245d8404784b9fbab9b439ac908>:0)
System.IO.StreamReader..ctor (System.String path, System.Boolean detectEncodingFromByteOrderMarks) (at <437ba245d8404784b9fbab9b439ac908>:0)
System.IO.StreamReader..ctor (System.String path) (at <437ba245d8404784b9fbab9b439ac908>:0)
(wrapper remoting-invoke-with-check) System.IO.StreamReader..ctor(string)
System.IO.File.ReadAllText (System.String path) (at <437ba245d8404784b9fbab9b439ac908>:0)
UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow.IsDirty () (at library/packagecache/com.unity.shadergraph@8.0.1/editor/drawing/materialgrapheditwindow.cs:256)
UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow.OnDestroy () (at library/packagecache/com.unity.shadergraph@8.0.1/editor/drawing/materialgrapheditwindow.cs:289)
UnityEditor.GenericMenu:CatchMenu(Object, String[], Int32)