[Bug] NullReferenceException during dotnet-gitversion execution

This one is a show stopper for the library. During the build we are getting NullReferenceException

System.NullReferenceException: Object reference not set to an instance of an object.
   at GitVersion.GitObject..ctor(GitObject innerGitObject) in D:\a\GitVersion\GitVersion\src\GitVersion.LibGit2Sharp\Git\GitObject.cs:line 12
   at GitVersion.Commit..ctor(Commit innerCommit) in D:\a\GitVersion\GitVersion\src\GitVersion.LibGit2Sharp\Git\Commit.cs:line 15
   at GitVersion.GitRepository.<>c__DisplayClass27_0.<FindMergeBase>b__0() in D:\a\GitVersion\GitVersion\src\GitVersion.LibGit2Sharp\Git\GitRepository.cs:line 60
   at Polly.Policy`1.<>c__DisplayClass11_0.<Execute>b__0(Context ctx, CancellationToken ct)
   at Polly.Retry.RetryEngine.Implementation[TResult](Func`3 action, Context context, CancellationToken cancellationToken, ExceptionPredicates shouldRetryExceptionPredicates, ResultPredicates`1 shouldRetryResultPredicates, Action`4 onRetry, Int32 permittedRetryCount, IEnumerable`1 sleepDurationsEnumerable, Func`4 sleepDurationProvider)
   at Polly.Retry.RetryPolicy`1.Implementation(Func`3 action, Context context, CancellationToken cancellationToken)
   at Polly.Policy`1.Execute(Func`3 action, Context context, CancellationToken cancellationToken)
   at Polly.Policy`1.Execute(Func`1 action)
   at GitVersion.Helpers.RetryAction`2.Execute(Func`1 operation) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Helpers\RetryAction.cs:line 42
   at GitVersion.GitRepository.FindMergeBase(ICommit commit, ICommit otherCommit) in D:\a\GitVersion\GitVersion\src\GitVersion.LibGit2Sharp\Git\GitRepository.cs:line 58
   at GitVersion.RepositoryStore.FindMergeBase(IBranch branch, IBranch otherBranch) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 46
   at GitVersion.RepositoryStore.<>c__DisplayClass29_0.<GetMergeCommitsForBranch>b__2(IBranch otherBranch) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 466
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.WhereEnumerableIterator`1.ToArray()
   at System.Linq.OrderedEnumerable`1.ToList()
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at GitVersion.RepositoryStore.GetMergeCommitsForBranch(IBranch branch, Config configuration, IEnumerable`1 excludedBranches) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 450
   at GitVersion.RepositoryStore.FindCommitBranchWasBranchedFrom(IBranch branch, Config configuration, IBranch[] excludedBranches) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 328
   at GitVersion.VersionCalculation.VersionInBranchNameVersionStrategy.GetVersions(String tagPrefixRegex, IBranch currentBranch)+MoveNext() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\BaseVersionCalculators\VersionInBranchNameVersionStrategy.cs:line 41
   at GitVersion.VersionCalculation.BaseVersionCalculator.GetBaseVersions(IVersionStrategy strategy)+MoveNext() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\BaseVersionCalculator.cs:line 90
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at GitVersion.VersionCalculation.BaseVersionCalculator.GetBaseVersion() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\BaseVersionCalculator.cs:line 31
   at GitVersion.VersionCalculation.NextVersionCalculator.FindVersion() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\NextVersionCalculator.cs:line 58
   at GitVersion.GitVersionCalculateTool.CalculateVersionVariables() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\GitVersionCalculateTool.cs:line 52
   at GitVersion.GitVersionExecutor.RunGitVersionTool(GitVersionOptions gitVersionOptions) in D:\a\GitVersion\GitVersion\src\GitVersion.App\GitVersionExecutor.cs:line 70
  INFO [06/17/21 19:06:23:48] Attempting to show the current git graph (please include in issue): 
  INFO [06/17/21 19:06:23:48] Showing max of 100 commits
  INFO [06/17/21 19:06:23:58] *   4cbc0d65 in the future  (HEAD -> release/5.12.0, origin/release/5.12.0)

Used GitVersion.TooL task when the problem first started, upgraded to GitVersion.MSBuild latest with no success. Switched to Actions in hope that will fix the issue, but it is all the same.

This is the link to failing build. To reproduce, just clone branch locally.

[pavelmateju]

@asbjornu ,

Yes you are right. My bad. This is another bug. Thank you !

As soon as you specified correct value or even some value you get expected result.

[asbjornu]

@pavelmateju, your problem is that the /output argument is missing a value. It failing with a NullReferenceException is a bug, but if you add /output json it works.