Had a project using version 1.0.0-beta-63127-02 and updated to 1.0.0-beta2-19351-01 and started experiencing this error. I have tried this on three different project types, .NET Standard and .NET Framework and it occurs on both. I also tried a .NET Standard with targetframeowrk set to net472 and same issue. These were all brand new projects in the same git repo.

Severity Code Description Project File Line Suppression State
Error MSB4018 The "Microsoft.Build.Tasks.Git.LocateRepository" task failed unexpectedly.
System.ArgumentNullException: Value cannot be null.
Parameter name: path1
at System.IO.Path.Combine(String path1, String path2)
at Microsoft.Build.Tasks.Git.GitEnvironment.FindSystemDirectory() in //src/Microsoft.Build.Tasks.Git/GitDataReader/GitEnvironment.cs:line 88
at Microsoft.Build.Tasks.Git.GitEnvironment.CreateFromProcessEnvironment() in //src/Microsoft.Build.Tasks.Git/GitDataReader/GitEnvironment.cs:line 79
at Microsoft.Build.Tasks.Git.GitEnvironment.Create(String configurationScope) in //src/Microsoft.Build.Tasks.Git/GitDataReader/GitEnvironment.cs:line 64
at Microsoft.Build.Tasks.Git.RepositoryTask.GetOrCreateRepositoryInstance() in //src/Microsoft.Build.Tasks.Git/RepositoryTask.cs:line 112
at Microsoft.Build.Tasks.Git.RepositoryTask.ExecuteImpl() in //src/Microsoft.Build.Tasks.Git/RepositoryTask.cs:line 65
at Microsoft.Build.Tasks.Git.RepositoryTask.Execute() in //src/Microsoft.Build.Tasks.Git/RepositoryTask.cs:line 43
at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
at Microsoft.Build.BackEnd.TaskBuilder.d__26.MoveNext() NuGetStandardTest C:\Users\wjvii.nuget\packages\microsoft.build.tasks.git\1.0.0-beta2-19351-01\build\Microsoft.Build.Tasks.Git.targets 24