Cannot generate OpenAPI Spec from .NET Core Assembly

[anas2204]

I'm trying to generate OpenAPI document from .NET Core 2.2 Assembly files.

Setup I've installed NSwag studio so "nswag" command is directly available from Command prompt. I've also built using the following way as recommended:

dotnet build /p:CopyLocalLockFileAssemblies=true

Error: Command Line

The error I get after using AspNetCore2OpenApi command is:

Command: aspnetcore2openapi /assembly:TestApi.dll /documentName:OpenApi3 /output:swagger.json

System.InvalidOperationException: The command 'aspnetcore2openapi /assembly:testapi.dll /documentname:openapi3 /output:swagger.json' could not be found.
   at NConsole.CommandLineProcessor.<ProcessSingleAsync>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at NConsole.CommandLineProcessor.<ProcessAsync>d__11.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at NConsole.CommandLineProcessor.Process(String[] args, Object input)
   at NSwag.Commands.NSwagCommandProcessor.Process(String[] args)

Error: NSwagStudio

The error displayed is:

System.NullReferenceException: Object reference not set to an instance of an object.

Runtime: NetCore22
   at CatalogApi.Extensions.HttpClientPolicyExtensions.AddPolicies(IServiceCollection services, IConfiguration configuration) in C:\Users\ansiddiq\Source\Repos\SS-ME-ES-APIC-CatalogService\Api\CatalogApi\Extensions\HttpClientPolicyExtensions.cs:line 36
   at CatalogApi.Startup.ConfigureServices(IServiceCollection services) in C:\Users\ansiddiq\Source\Repos\SS-ME-ES-APIC-CatalogService\Api\CatalogApi\Startup.cs:line 102
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceCollection services)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.Initialize()
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
   at NSwag.Commands.Generation.OpenApiGeneratorCommandBase`1.CreateWebHostAsync(AssemblyLoader assemblyLoader) in C:\projects\nswag\src\NSwag.Commands\Commands\Generation\OpenApiGeneratorCommandBase.cs:line 318
   at NSwag.Commands.Generation.AspNetCore.AspNetCoreToSwaggerCommand.RunIsolatedAsync(AssemblyLoader assemblyLoader) in C:\projects\nswag\src\NSwag.Commands\Commands\Generation\AspNetCore\AspNetCoreToOpenApiCommand.cs:line 309
   at NSwag.Commands.IsolatedCommandBase`1.IsolatedCommandAssemblyLoader`1.Run(String commandType, String commandData, String[] assemblyPaths, String[] referencePaths) in C:\projects\nswag\src\NSwag.Commands\Commands\IsolatedCommandBase.cs:line 71
   at NSwag.Commands.IsolatedCommandBase`1.<>c__DisplayClass17_0.<RunIsolatedAsync>b__0() in C:\projects\nswag\src\NSwag.Commands\Commands\IsolatedCommandBase.cs:line 61
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)
--- End of stack trace from previous location where exception was thrown ---
   at NSwag.Commands.IsolatedCommandBase`1.RunIsolatedAsync(String configurationFile)
   at NSwag.Commands.IsolatedSwaggerOutputCommandBase`1.RunAsync(CommandLineProcessor processor, IConsoleHost host) in C:\projects\nswag\src\NSwag.Commands\Commands\IsolatedSwaggerOutputCommandBase.cs:line 47
   at NSwag.Commands.Generation.AspNetCore.AspNetCoreToSwaggerCommand.RunAsync(CommandLineProcessor processor, IConsoleHost host) in C:\projects\nswag\src\NSwag.Commands\Commands\Generation\AspNetCore\AspNetCoreToOpenApiCommand.cs:line 94
   at NSwag.Commands.NSwagDocumentBase.GenerateSwaggerDocumentAsync() in C:\projects\nswag\src\NSwag.Commands\NSwagDocumentBase.cs:line 279
   at NSwag.Commands.NSwagDocument.ExecuteAsync() in C:\projects\nswag\src\NSwag.Commands\NSwagDocument.cs:line 81
   at NSwag.Commands.Document.ExecuteDocumentCommand.ExecuteDocumentAsync(IConsoleHost host, String filePath) in C:\projects\nswag\src\NSwag.Commands\Commands\Document\ExecuteDocumentCommand.cs:line 85
   at NSwag.Commands.Document.ExecuteDocumentCommand.RunAsync(CommandLineProcessor processor, IConsoleHost host) in C:\projects\nswag\src\NSwag.Commands\Commands\Document\ExecuteDocumentCommand.cs:line 32
   at NConsole.CommandLineProcessor.ProcessSingleAsync(String[] args, Object input)
   at NConsole.CommandLineProcessor.ProcessAsync(String[] args, Object input)
   at NConsole.CommandLineProcessor.Process(String[] args, Object input)
   at NSwag.Commands.NSwagCommandProcessor.Process(String[] args) in C:\projects\nswag\src\NSwag.Commands\NSwagCommandProcessor.cs:line 56

This error seems to be in a file where I use "Polly" library in Middleware for HTTP Retry logic. There is no problem in the code as it compiles/runs fine.

Any help is appreciated!