Swagger not working in 4.2.0

Greetings:

Today I noticed there was a new version of this awesome library and installed it right away. Just after that my API refused to start, giving me this trace error:

System.ArgumentNullException: Value cannot be null. (Parameter 'provider')
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.CreateScope(IServiceProvider provider)
   at FastEndpoints.Swagger.ValidationSchemaProcessor..ctor()
   at FastEndpoints.Swagger.Extensions.EnableFastEndpoints(AspNetCoreOpenApiDocumentGeneratorSettings settings, Int32 tagIndex, Int32 maxEndpointVersion, Boolean shortSchemaNames)
   at FastEndpoints.Swagger.Extensions.<>c__DisplayClass2_0.<AddSwaggerDoc>b__0(AspNetCoreOpenApiDocumentGeneratorSettings s)
   at Microsoft.Extensions.DependencyInjection.NSwagServiceCollectionExtensions.<>c__DisplayClass0_0.<AddOpenApiDocument>b__0(AspNetCoreOpenApiDocumentGeneratorSettings settings, IServiceProvider services)
   at Microsoft.Extensions.DependencyInjection.NSwagServiceCollectionExtensions.<>c__DisplayClass1_0.<AddOpenApiDocument>b__0(AspNetCoreOpenApiDocumentGeneratorSettings settings, IServiceProvider services)
   at Microsoft.Extensions.DependencyInjection.NSwagServiceCollectionExtensions.<>c__DisplayClass3_0.<AddSwaggerDocument>b__0(IServiceProvider services)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(Type serviceType)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.AspNetCore.Builder.NSwagApplicationBuilderExtensions.UseOpenApiWithApiExplorerCore(IApplicationBuilder app, Action`1 configure)
   at Microsoft.AspNetCore.Builder.NSwagApplicationBuilderExtensions.UseOpenApi(IApplicationBuilder app, Action`1 configure)
   at Program.<Main>$(String[] args) 

The execution stops at: app.UseOpenApi();

If I remove:
app.UseOpenApi();
app.UseSwaggerUi3();

the api starts and works just fine, this is swagger related only, I think.

Maybe the fault is in my end? Going back to 4.1.0 fixes the problem without changing any code.

Best Regards.

[wjax]

static IServiceProvider ServiceProvider { get; set; } //set only from .UseFastEndpoints() during startup

Yeah, I think is there

[dj-nitehawk]

@desarrollo-ctme & @wjax i believe i’ve figured out what’s happening. most likely you’re calling app.UseOpenApi() before calling app.UseFastEndpoints() like so:

var builder = WebApplication.CreateBuilder();
builder.Services.AddFastEndpoints();
builder.Services.AddSwaggerDoc();

var app = builder.Build();
app.UseAuthorization();
app.UseOpenApi();
app.UseFastEndpoints(); //this reproduces the null reference exception - move this up to fix the issue
app.UseSwaggerUi3(s => s.ConfigureDefaults());
app.Run();

i will add better checks against this and throw a proper error message when the pipeline is configured incorrectly like this.

if that doesn’t solve it for you, please do a repo that has the problem so we can clone it and debug.

thanks!