[Bug] failure when a branch with `--allow-unrelated-histories` is merged in the repository

[jeromelaban]

Describe the bug

The following happens when processing a branch in the repository that is merged with a common ancestor for all other branches and the --allow-unrelated-histories flag is used. This merged branch does not need to be the one being versioned, only to be present in the repository.

Expected Behavior

Gitversion finishes properly.

Actual Behavior

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 14
   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 61
   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 GitVersion.RepositoryStore.FindMergeBase(IBranch branch, IBranch otherBranch) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 34
   at GitVersion.RepositoryStore.<>c__DisplayClass29_0.<GetMergeCommitsForBranch>b__2(IBranch otherBranch) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\RepositoryStore.cs:line 460
   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.Configuration.BranchConfigurationCalculator.InheritBranchConfiguration(IBranch targetBranch, BranchConfig branchConfiguration, ICommit currentCommit, Config configuration, IList`1 excludedInheritBranches) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Configuration\BranchConfigurationCalculator.cs:line 81
   at GitVersion.Configuration.BranchConfigurationCalculator.GetBranchConfiguration(IBranch targetBranch, ICommit currentCommit, Config configuration, IList`1 excludedInheritBranches) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Configuration\BranchConfigurationCalculator.cs:line 47
   at GitVersion.GitVersionContextFactory.Create(GitVersionOptions gitVersionOptions) in D:\a\GitVersion\GitVersion\src\GitVersion.Core\Core\GitVersionContextFactory.cs:line 40
   at GitVersion.GitVersionCoreModule.<>c__DisplayClass0_0.<RegisterTypes>b__1() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\GitVersionCoreModule.cs:line 38
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at GitVersion.VersionCalculation.NextVersionCalculator.get_context() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\NextVersionCalculator.cs:line 17
   at GitVersion.VersionCalculation.NextVersionCalculator.FindVersion() in D:\a\GitVersion\GitVersion\src\GitVersion.Core\VersionCalculation\NextVersionCalculator.cs:line 32
   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 61

Possible Fix

Steps to Reproduce

I'm not sure exacty sure how to reproduce this, but this seems to happen when trying to build the version for a branch that dependabot is building.

Here's the config file used, if that helps.

Your Environment

Azure devops windows, mac and linux hosted agents.

[asbjornu]

Are you able to reproduce this in a publicly available repository?

[github-actions]

🎉 This issue has been resolved in version 5.10.0 🎉
The release is available on:

• GitHub Release
• Chocolatey Package
• .Net Global Tool

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