title: VSTS fails to build; error MSB4184: The expression "[System.IO.Path]::GetDirectoryName('')" cannot be evaluated. The path is not of a legal form
body: <p>I am trying to build my .Net Core solution and I am getting these error messages that I can't figure out;</p>
  
  <pre><code>2017-05-22T14:30:56.2490242Z _TransformWebConfig:
  2017-05-22T14:30:56.2490242Z   No web.config found. Creating 'd:\a\1\s\SIR\obj\Release\net452\win7-x86\PubTmp\Out\web.config'
  2017-05-22T14:30:56.2830092Z ##[error]C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk.Publish\build\netstandard1.0\PublishTargets\Microsoft.NET.Sdk.Publish.MSDeployPackage.targets(124,7): Error MSB4184: The expression "[System.IO.Path]::GetDirectoryName('')" cannot be evaluated. The path is not of a legal form.
  2017-05-22T14:30:56.2830092Z ##[debug]Processed: ##vso[task.logissue type=Error;sourcepath=C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk.Publish\build\netstandard1.0\PublishTargets\Microsoft.NET.Sdk.Publish.MSDeployPackage.targets;linenumber=124;columnnumber=7;code=MSB4184;]The expression "[System.IO.Path]::GetDirectoryName('')" cannot be evaluated. The path is not of a legal form.
  2017-05-22T14:30:56.2830092Z C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk.Publish\build\netstandard1.0\PublishTargets\Microsoft.NET.Sdk.Publish.MSDeployPackage.targets(124,7): error MSB4184: The expression "[System.IO.Path]::GetDirectoryName('')" cannot be evaluated. The path is not of a legal form. [d:\a\1\s\SIR\Properties.API.csproj]
  2017-05-22T14:30:56.2830092Z ##[debug]Processed: ##vso[task.logdetail id=43c372fe-1339-4917-bfb2-2d3438740b01;parentid=e8365874-6f54-4a8c-a31f-62c69bcfdb57;type=Build;result=Failed;finishtime=2017-05-22T14:30:56.2790105Z;progress=100;state=Completed;parentid=e8365874-6f54-4a8c-a31f-62c69bcfdb57;name=;]
  2017-05-22T14:30:56.2830092Z Done Building Project "d:\a\1\s\SIR\Properties.API.csproj" (default targets) -- FAILED.
  </code></pre>