use old nuget version
There seems to be a bug introduced in 5.9.1. Let us downgrade to 5.7.1.
I can reproduce the pipeline error locally getting a stacktrace like this:
$ nuget.exe pack OpenTAP.nuspec -OutputDirectory .. -Verbosity detailed
NuGet Version: 5.9.1.11
Attempting to build package from 'OpenTAP.nuspec'.
Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
at NuGet.Packaging.PackageBuilder.<>c.<ValidateReferenceAssemblies>b__173_1(NuGet.Frameworks1204671.NuGetFramework groupFramework)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.HashSet`1.UnionWith(IEnumerable`1 other)
at System.Collections.Generic.HashSet`1..ctor(IEnumerable`1 collection, IEqualityComparer`1 comparer)
at NuGet.Packaging.PackageBuilder.ValidateReferenceAssemblies(IEnumerable`1 files, IEnumerable`1 packageAssemblyReferences)
at NuGet.Packaging.PackageBuilder.Save(Stream stream)
at NuGet.Commands.PackCommandRunner.BuildPackage(PackageBuilder builder, String outputPath, Boolean symbolsPackage)
at NuGet.Commands.PackCommandRunner.BuildFromNuspec(String path)
at NuGet.CommandLine.PackCommand.ExecuteCommand()
at NuGet.CommandLine.Command.ExecuteCommandAsync()
at NuGet.CommandLine.Command.Execute()
at NuGet.CommandLine.Program.MainCore(String workingDirectory, String[] args)
I tried attaching the debugger but the error doesn't really make that much sense to me. Let us just downgrade to 5.7.1 for now
Closes #653 (closed)