When "Package Manager" window is docked in the editor and entered in play mode, Package Manager window turns black and NullReferenceException is thrown in the console also Even if you close the packman window and reopen it would throw errors and a black screen, refer attached video.

Steps to Reproduce:
1. Create a New Project with 2D Template
2. Window > Package Manager > Docked
3. Hit play

Actual Result:
NullReferenceException is thrown and "Package Manager" window turns black

Expected:
Editor enters in play mode gracefully

Workaround: Reimport project

Reproducible on:
2020.2.0a5

Working fine on:
2020.2.0a4, 2020.1.0b3

Package Found version: 4.2.1, 4.1.0, 3.0.8, 3.0.5, 3.0.2

Environment:
Windows 10 and macOS 10.14

Stack trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PackageManager.UI.Sample.get_size () (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageSampleItem..ctor (UnityEditor.PackageManager.UI.IPackageVersion version, UnityEditor.PackageManager.UI.Sample sample) (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageSampleList.SetPackageVersion (UnityEditor.PackageManager.UI.IPackageVersion version) (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageDetails.SetDisplayVersion (UnityEditor.PackageManager.UI.IPackageVersion version) (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageDetails.SetPackage (UnityEditor.PackageManager.UI.IPackage package, UnityEditor.PackageManager.UI.IPackageVersion version) (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageDetails.OnSelectionChanged (UnityEditor.PackageManager.UI.IPackageVersion version) (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageDetails.OnEnable () (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.PackageManagerWindow.OnEnable () (at <89faf899e9c14826b38ffd64a0c1974d>:0)
UnityEditor.PackageManager.UI.Window:ShowPackageManagerWindow(MenuCommand)