title: '' is not a valid version string." exception in nuget for VS2019
body: <p>I have installed VS 2019 today removing all other versions of VS (over come space crunch). Am trying to use nuget package manager but keep getting below exception. Nothing loads. I tried to install packages from console and ended up with same error as below.
  Any help would be appreciated.</p>
  
  <p>PM> Install-Package Microsoft.Azure.Devices -Version 1.21.0
  Install-Package : <strong>'' is not a valid version string.</strong>
  At line:1 char:1
  + Install-Package Microsoft.Azure.Devices -Version 1.21.0
  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      + CategoryInfo          : NotSpecified: (:) [Install-Package], Exception
      + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PackageManagement.PowerShellCmdlets.InstallPackageCommand</p>
  
  <p>Time Elapsed: 00:00:00.6338016</p>