NSwag (Command-Line OR Studio) not generating Swagger from Assembly - asp.net-core

Question

Problem:
I wish to generate a Swagger file (Open API document) from an ASP.NET Core 2.2 Web API project (either from the solution file or Compiled assemblies).
Everything is tried using the NSwag tools.
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
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!