Improve the error reported in the log for a NullReferenceException issue

509行目のReferenceTrackSchemasにあるServiceDefinition.csから始め、次に321行目のCompare、34行目のSwaggerModeler.csを追ってください。エラーの詳細に示されているold/newの解決済みファイルと、OpenApiDiff.dllコマンドを使用して失敗を再現してください。ログに、NullReferenceExceptionだけでなく、基になる仕様の問題を追跡できる十分なコンテキストが記録されれば完了です。

The following error seems to be caused by spec issues, but it doesn't have enough information to trace the real issues.

Error: appendOadRuntimeErrors: {"type":"Raw","level":"Error","message":"Runtime Exception","time":"2025-08-06T20:28:16.228Z","groupName":"preview","extra":{"new":"https://github.com/stevemunk/azure-rest-api-specs/blob/ec36d0206de5a236b79e079611bcd25df47362cd/specification/maps/data-plane/Microsoft.Maps/Alias/preview/2.0/alias.json","old":"https://github.com/Azure/azure-rest-api-specs/blob/main/specification/maps/data-plane/Microsoft.Maps/Alias/preview/2.0/alias.json","details":"Command failed: dotnet /home/runner/work/azure-rest-api-specs/azure-rest-api-specs/node_modules/\\@azure/oad/dlls/OpenApiDiff.dll -o /tmp/oad-6bw2a3/old-resolved.json -n /tmp/oad-2X5zP2/new-resolved.json\nUnhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.\n   at AutoRest.Swagger.Model.ServiceDefinition.ReferenceTrackSchemas(ServiceDefinition service) in D:\\a\\_work\\1\\s\\openapi-diff\\src\\modeler\\AutoRest.Swagger\\Model\\ServiceDefinition.cs:line 509\n   at AutoRest.Swagger.Model.ServiceDefinition.Compare(ComparisonContext`1 context, ServiceDefinition previousDefinition) in D:\\a\\_work\\1\\s\\openapi-diff\\src\\modeler\\AutoRest.Swagger\\Model\\ServiceDefinition.cs:line 321\n   at AutoRest.Swagger.SwaggerModeler.Compare(String fileNameOld, String swaggerOld, String fileNameNew, String swaggerNew, Settings settings) in D:\\a\\_work\\1\\s\\openapi-diff\\src\\modeler\\AutoRest.Swagger\\SwaggerModeler.cs:line 34\n   at OpenApiDiff.Program.Main(String[] args) in D:\\a\\_work\\1\\s\\openapi-diff"}}

Pipeline run:
https://github.com/Azure/azure-rest-api-specs/actions/runs/16787747592/job/47542471322?pr=36493