MSBuildSdkExtras: Profile328 doesn't work

Per Stephen Mccleary’s blog which your readme references, I tried to add portable-net4+sl50+win8+wpa81+wp8 as a target framework, but I get these build errors when I do so:

C:\Program Files (x86)\Microsoft Visual Studio\2017\d15rel\MSBuild\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.TargetFrameworkInference.targets(84,5): error : Cannot infer TargetFram eworkIdentifier and/or TargetFrameworkVersion from TargetFramework=‘portable-net4+sl50+win8+wpa81+wp8’. They must be specified explicitly. [C:\git\Validation.my\src\Validation\Valid ation.csproj] C:\Program Files (x86)\Microsoft Visual Studio\2017\d15rel\MSBuild\15.0\bin\Microsoft.Common.CurrentVersion.targets(1111,5): error MSB3644: The reference assemblies for framework “. NETFramework,Version=v0.0” were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework f or which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend. [C:\git\Validation.my\src\Validation\Validation.csproj]