ArgumentNullException in newer version of docfx NuGet (2.49)

[wiwei]

Operation System: Windows

DocFX Version Used: 2.49

Template used: default

Steps to Reproduce:
Run docfx docfx.json -f on the following project:

https://github.com/microsoft/MixedRealityToolkit-Unity/blob/mrtk_development/docfx.json

https://dev.azure.com/aipmr/MixedRealityToolkit-Unity-CI/_build/results?buildId=9516&view=logs&j=275f1d19-1bd8-5591-b06b-07d489ea915a&t=a4822bc1-f3a9-5984-c941-6c1b7aa2ab81

Note that this seems to be a regression in the latest docfx NuGet package. We previously were using the latest (2.48.1) which was working fine, and after pulling the newer package (2.49) this issue started happening. To work around this we're forcing our infrastructure to use an older version (i.e. 2.48.1) which is still working fine for us.

Expected Behavior:
No exception

Actual Behavior:
2020-02-18T18:04:54.4278760Z Parameter name: key
2020-02-18T18:04:54.4279171Z at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
2020-02-18T18:04:54.4279350Z at System.Collections.Generic.Dictionary2.FindEntry(TKey key) 2020-02-18T18:04:54.4279504Z at System.Collections.Generic.Dictionary2.TryGetValue(TKey key, TValue& value)
2020-02-18T18:04:54.4279710Z at Microsoft.DocAsCode.Metadata.ManagedReference.CopyInherited.Copy(MetadataItem dest, String srcName, ResolverContext context)
2020-02-18T18:04:54.4279934Z at Microsoft.DocAsCode.Metadata.ManagedReference.CopyInherited.InheritDoc(MetadataItem dest, ResolverContext context)
2020-02-18T18:04:54.4280101Z at Microsoft.DocAsCode.Metadata.ManagedReference.CopyInherited.<>c__DisplayClass0_0.b__1(MetadataItem current, MetadataItem parent)
2020-02-18T18:04:54.4280283Z at Microsoft.DocAsCode.Common.TreeIterator.Preorder[T](T current, T parent, Func2 childrenGetter, Func3 action)
2020-02-18T18:04:54.4280473Z at Microsoft.DocAsCode.Common.TreeIterator.Preorder[T](T current, T parent, Func2 childrenGetter, Func3 action)
2020-02-18T18:04:54.4280633Z at Microsoft.DocAsCode.Common.TreeIterator.Preorder[T](T current, T parent, Func2 childrenGetter, Func3 action)
2020-02-18T18:04:54.4280870Z at Microsoft.DocAsCode.Common.TreeIterator.Preorder[T](T current, T parent, Func2 childrenGetter, Func3 action)
2020-02-18T18:04:54.4281192Z at Microsoft.DocAsCode.Metadata.ManagedReference.CopyInherited.Run(MetadataModel yaml, ResolverContext context)
2020-02-18T18:04:54.4281410Z at Microsoft.DocAsCode.Metadata.ManagedReference.YamlMetadataResolver.ExecutePipeline(MetadataModel yaml, ResolverContext context)
2020-02-18T18:04:54.4281664Z at Microsoft.DocAsCode.Metadata.ManagedReference.YamlMetadataResolver.ResolveMetadata(Dictionary2 allMembers, Dictionary2 allReferences, Boolean preserveRawInlineComments)
2020-02-18T18:04:54.4281929Z at Microsoft.DocAsCode.Metadata.ManagedReference.ExtractMetadataWorker.d__19.MoveNext()
2020-02-18T18:04:54.4282140Z at System.Collections.Generic.List1..ctor(IEnumerable1 collection)
2020-02-18T18:04:54.4282329Z at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
2020-02-18T18:04:54.4282543Z at Microsoft.DocAsCode.Metadata.ManagedReference.ExtractMetadataWorker.d__13.MoveNext()
2020-02-18T18:04:54.4282833Z --- End of stack trace from previous location where exception was thrown ---
2020-02-18T18:04:54.4282986Z at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
2020-02-18T18:04:54.4283139Z at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
2020-02-18T18:04:54.4283291Z at Microsoft.DocAsCode.Metadata.ManagedReference.ExtractMetadataWorker.d__11.MoveNext()
2020-02-18T18:04:54.4283488Z 0 Warning(s)
2020-02-18T18:04:54.4283593Z 1 Error(s)

[tstivers1990]

Also experiencing this issue.

[nike4613]

Also experiencing this issue with DocFX 2.49 from Chocolatey.

[wiwei]

@yufeih @mingwli have you guys considered rolling back the latest version? It seems like it's causing trouble for a lot of consumers out there judging by the number of duplicate issues and other confirmations.

[superyyrrzz]

@wiwei #5561 should fix this. Could you try DocFX >= 2.50?