Solution to 'Value cannot be null. Parameter name: path1' with dotnet and tox

C:\Program Files\dotnet\sdk\2.0.0\NuGet.targets(466,5): error : Value cannot be null.
C:\Program Files\dotnet\sdk\2.0.0\NuGet.targets(466,5): error : Parameter name: path1

```text
```bash

System.ArgumentNullException: Value cannot be null.
Parameter name: path1
   at System.IO.Path.Combine(String path1, String path2)
   at Microsoft.DotNet.Configurer.CliFallbackFolderPathCalculator.get_DotnetUserProfileFolderPath()
   at Microsoft.DotNet.Configurer.FirstTimeUseNoticeSentinel..ctor(CliFallbackFolderPathCalculator cliFallbackFolderPathCalculator)
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, ITelemetry telemetryClient)
   at Microsoft.DotNet.Cli.Program.Main(String[] args)

```text

That is happening because all environment variables are not passed to tox by default.

Open `tox.ini` and add the `passenv = APPDATA ProgramFiles USERPROFILE` line:

```bash

[testenv]
setenv =
    PYTHONPATH = {toxinidir}

commands =
    python setup.py test

passenv = APPDATA ProgramFiles USERPROFILE