Null Reference exception occurs and package manager window disappears on updating it.

Steps to Repro:
1. Open attached or create a new project
2. Window > Package manager
3. Go to In project tab > package manager UI
4. Update to latest version

Actual Result:
1. Package manager window restarts
2. The UI is not visible in the window
3. Null reference exception occurs
4. UI appears on reopening the window
5. Sometimes UI doesn't appear back

Workaround:
1. Go to Help
2. Reset packages to default

Expected Result:
1. Package manager window should gracefully restart

Occurring with:
2018.1.0f2, 2018.1.0f1, 2018.1.0b10, 2018.1.0b5

Note: UI is loading with 2018.2.0b2 however the error still occurs

Environment:
Windows & Mac

Stack Trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PackageManager.UI.PackageDetails..ctor () (at C:/Users/GS1793/AppData/Local/Unity/cache/packages/packages.unity.com/com.unity.package-manager-ui@1.9.6/Editor/Sources/UI/PackageDetails.cs:81)
UnityEditor.PackageManager.UI.PackageDetailsFactory.DoCreate (IUxmlAttributes bag, CreationContext cc) (at C:/Users/GS1793/AppData/Local/Unity/cache/packages/packages.unity.com/com.unity.package-manager-ui@1.9.6/Editor/Sources/UI/PackageDetails.cs:19)
UnityEngine.Experimental.UIElements.UxmlFactory`1[T].Create (IUxmlAttributes bag, CreationContext cc) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualElementFactory.cs:19)
UnityEngine.Experimental.UIElements.VisualElementAsset.Create (CreationContext ctx) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualElementAsset.cs:116)
UnityEngine.Experimental.UIElements.VisualTreeAsset.CloneSetupRecursively (UnityEngine.Experimental.UIElements.VisualElementAsset root, System.Collections.Generic.Dictionary`2 idToChildren, CreationContext context) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualTreeAsset.cs:154)
UnityEngine.Experimental.UIElements.VisualTreeAsset.CloneSetupRecursively (UnityEngine.Experimental.UIElements.VisualElementAsset root, System.Collections.Generic.Dictionary`2 idToChildren, CreationContext context) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualTreeAsset.cs:203)
UnityEngine.Experimental.UIElements.VisualTreeAsset.CloneSetupRecursively (UnityEngine.Experimental.UIElements.VisualElementAsset root, System.Collections.Generic.Dictionary`2 idToChildren, CreationContext context) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualTreeAsset.cs:203)
UnityEngine.Experimental.UIElements.VisualTreeAsset.CloneTree (UnityEngine.Experimental.UIElements.VisualElement target, System.Collections.Generic.Dictionary`2 slotInsertionPoints) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualTreeAsset.cs:143)
UnityEngine.Experimental.UIElements.VisualTreeAsset.CloneTree (System.Collections.Generic.Dictionary`2 slotInsertionPoints) (at C:/buildslave/unity/build/Modules/UIElements/UXML/VisualTreeAsset.cs:108)
UnityEditor.PackageManager.UI.PackageManagerWindow.OnEnable () (at C:/Users/GS1793/AppData/Local/Unity/cache/packages/packages.unity.com/com.unity.package-manager-ui@1.9.6/Editor/Sources/UI/PackageManagerWindow.cs:26)