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Tag: nullable-reference-types

2 posts

2026-10-20 aspnetcore openapi dotnet-11

How to mark a controller action's response as nullable in ASP.NET Core's built-in OpenAPI document

Microsoft.AspNetCore.OpenApi only marks a response nullable when the action returns a bare T? (and, on .NET 10, not even Task<T?>). ActionResult<T?> and IActionResult lose the annotation on both .NET 10 and .NET 11 RC2. Here is why, a tested operation transformer that fixes it, and the 204 No Content trap that makes the spec lie unless you also change MVC's formatter.

2026-09-25 errors aspnetcore dotnet-10

Fix: ASP.NET Core returns 400 "The X field is required" for a non-nullable string property

With <Nullable>enable</Nullable>, MVC treats every non-nullable reference type as [Required(AllowEmptyStrings = true)]. Mark optional properties as string?, give them a default, or set SuppressImplicitRequiredAttributeForNonNullableReferenceTypes.