.NET 9 breaks ShouldSerializeXXX methods in data model (NullReferenceException)

[arisewanggithub]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

We are currently using .net 8 and we are upgrading to .net 9. But with the upgrade, our service can't start because some ShouldSerializeXXX methods throw NullReferenceException. e.g.

And from stacktrace, I can see the ShouldSerializeXXX methods are called from here in namespace Newtonsoft.Json.Serialization:

Microsoft.AspNetCore.Mvc.NewtonsoftJson has already been upgraded to 9.0.0
This works fine in .net 8 but breaks in .net 9

Expected Behavior

NullReferenceException should not be thrown when start the service

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

9.0.101

Anything else?

No response

[BrennanConroy]

What makes this a .NET or ASP.NET Core issue? The method you're pointing at is part of Newtonsoft.Json.
https://github.com/JamesNK/Newtonsoft.Json/blob/9317d71ac5f08c354060bad2cd9bfe6ed5856294/Src/Newtonsoft.Json/Serialization/DefaultContractResolver.cs#L1646

If you think it is an ASP.NET Core issue, please provide a minimal repro project.

[arisewanggithub]

WebApiTest.zip
I've created a minimum web service that can repro this. From the stack trace, I think the issue is triggered when NSwag OpenAPI documentation is generated on service startup. The same code works in .net 8 but not in .net 9.

[BrennanConroy]

Please provide the project as a github repo not a zip
https://github.com/dotnet/aspnetcore/blob/main/docs/repro.md#what-is-a-minimal-repro-project

[arisewanggithub]

OK, here is the github repo link: https://github.com/arisewanggithub/dotnetissue59402

[martincostello]

From the stack trace, I think the issue is triggered when NSwag OpenAPI documentation is generated on service startup

Maybe it's an NSwag issue?

[BrennanConroy]

Yeah, this looks like an NSwag issue. Closing as I don't see anything from ASP.NET Core in the stack.

[arisewanggithub]

OK, I created a new issue on NSWag for this: RicoSuter/NSwag#5065