Docked Look Dev window closes along with NullReferenceException error on entering Play mode.

Steps to repro:
1. Create a new HDRP template project
2. Windows > Render Pipeline > Look Dev
3. Docked the window > Enter the Play Mode.

Actual Result:
-NullReferenceException error is thrown in the console.

Expected Result:
-No errors in the console.

Reproducible in:
2020.2.0a18, 2020.1.0b16, 2020.1.0b6 with 9.0.0, 8.2.0, 8.1.0.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stack trace:
NullReferenceException: Object reference not set to an instance of an object
at UnityEditor.UIElements.DefaultEditorWindowBackend.PlayModeStateChangedCallback (UnityEditor.PlayModeStateChange state) [0x00017] in C:\buildslave\unity\build\Editor\Mono\UIElements\WindowBackends\DefaultEditorWindowBackend.cs:218
at (wrapper delegate-invoke) System.Action`1[UnityEditor.PlayModeStateChange].invoke_void_T(UnityEditor.PlayModeStateChange)
at UnityEditor.EditorApplication.Internal_PlayModeStateChanged (UnityEditor.PlayModeStateChange state) [0x00012] in C:\buildslave\unity\build\Editor\Mono\EditorApplication.cs:408