OpenApi generation OpenApiSchemaComparer fails with null values for Properties, AllOf, or AnyOf

[FrankSzendzielarz]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

OpenApiSchemaComparer uses code like hashCode.Add(obj.Properties.Count); . In custom schema transforms where I might want to replace allof , anyof, or properties, intuitively I would set unwanted properties to null. Either the setter should prevent this, or the obj.Properties.Count should be obj.Properties?.Count??0 or otherwise take care of nulls.

Expected Behavior

Not crash when a schema property is null.

Steps To Reproduce

Custom schema transform - set Properties to null. OpenApi doc gen and Scalar result have missing elements.

Exceptions (if any)

Object reference not set to an instance of an object.

.NET Version

9

Anything else?

No response

[captainsafia]

@FrankSzendzielarz Thanks for filing this issue!

I believe as a temporary workaround you can initialize the designated properties to empty lists. The OpenAPI document writer should do the write thing and not emit them but let me know if that's not the case.

With regard to how we might solve this in the long-term, with the adoption of Microsoft.OpenApi v2, we're hoping to move forward with the comparers being implemented in the library themselves (instead of in the ASP.NET Core codebase). There's also some changes coming to the nullability/default blues for collection-based properties like AllOf and friends.

I'll take this one as a sub-issue under #58619 for now since the comparers are removed from source in #59480.

[gumbarros]

I'm having the same exception but my Properties are never null. Any guidance?

Serilog.AspNetCore.RequestLoggingMiddleware
HTTP "GET" "/openapi/v1.json" responded 500 in 125.9134 ms
Show Exception

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaComparer.GetHashCode(OpenApiSchema obj)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaComparer.GetHashCode(OpenApiSchema obj)
   at System.Collections.Concurrent.ConcurrentDictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaReferenceTransformer.ResolveReferenceForSchema(OpenApiSchema schema, ConcurrentDictionary`2 schemasByReference, Boolean isTopLevel)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaReferenceTransformer.TransformAsync(OpenApiDocument document, OpenApiDocumentTransformerContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.ApplyTransformersAsync(OpenApiDocument document, IServiceProvider scopedServiceProvider, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiDocumentAsync(IServiceProvider scopedServiceProvider, HttpRequest httpRequest, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiDocumentAsync(IServiceProvider scopedServiceProvider, HttpRequest httpRequest, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Builder.OpenApiEndpointRouteBuilderExtensions.<>c__DisplayClass0_0.<<MapOpenApi>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F56B68D2B55B5B7B373BA2E4796D897848BC0F04A969B1AF6260183E8B9E0BAF2__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass2_0.<<MapGet0>g__RequestHandler|5>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.ResponseCaching.ResponseCachingMiddleware.Invoke(HttpContext httpContext)
   at Serilog.AspNetCore.RequestLoggingMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddlewareImpl.<Invoke>g__Awaited|10_0(ExceptionHandlerMiddlewareImpl middleware, HttpContext context, Task task)