RDG010: InvalidAsParameters Nullable

	Value
Rule ID	RDG010
Fix is breaking or non-breaking	Non-breaking

Cause

This diagnostic is emitted by the Request Delegate Generator when an endpoint contains a route handler with a parameter annotated with the [AsParameters] attribute that is marked as nullable.

Rule description

The implementation of surrogate binding via the [AsParameters] attribute in Minimal APIs only supports types that are not nullable.

using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateSlimBuilder(args);
builder.Services.ConfigureHttpJsonOptions(options =>
{
    options.SerializerOptions.TypeInfoResolverChain.Insert(0,
                                 AppJsonSerializerContext.Default);
});

var app = builder.Build();

app.MapGet("/todos/{id}", ([AsParameters] TodoRequest? request)
    => Results.Ok(new Todo(request!.Id)));

app.Run();

public record TodoRequest(HttpContext HttpContext, [FromRoute] int Id);
public record Todo(int Id);
[JsonSerializable(typeof(Todo[]))]
internal partial class AppJsonSerializerContext : JsonSerializerContext
{

}

How to fix violations

Declare the parameter as non-nullable.

using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateSlimBuilder(args);
builder.Services.ConfigureHttpJsonOptions(options =>
{
    options.SerializerOptions.TypeInfoResolverChain.Insert(0,
                                 AppJsonSerializerContext.Default);
});

var app = builder.Build();

app.MapGet("/todos/{id}", ([AsParameters] TodoRequest request)
    => Results.Ok(new Todo(request.Id)));

app.Run();

public record TodoRequest(HttpContext HttpContext, [FromRoute] int Id);
public record Todo(int Id);
[JsonSerializable(typeof(Todo[]))]
internal partial class AppJsonSerializerContext : JsonSerializerContext
{

}

When to suppress warnings

This warning should not be suppressed. Suppressing the warning leads to a runtime exception associated with the same warning.