Minimal API : Converting empty string to Nullable (ex: bool?) with [FromQuery] binding

[saithis]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

With a Minimal API endpoint like this:

app.MapGet("foobar", ([FromQuery] bool? myBool) => Results.Ok());

When I call it like this:

https://my.domain/foobar?myBool=
I get a 500 internal server error.

With controllers this worked just fine and myBool was null.

I saw a somewhat similar issue, that is already closed: #55202 but either it is wrongly closed or it was just fixed for [FromForm].

The linked PR introduced this check:

aspnetcore/src/Components/Endpoints/src/FormMapping/Converters/NullableConverter.cs

Line 61 in 1fd3d6a

return Type.GetTypeCode(type) != TypeCode.Object || IsSupportedUnderlyingObjectType(type);

But Type.GetTypeCode(typeof(bool?) returns Object, so this code shouldn't even work for [FromForm] with bool?, int?, etc.

Expected Behavior

I would have expected that ?myBool= would result in null if myBool is nullable.

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

10.0.103

Anything else?

No response

[saithis]

Would this be an acceptable solution?

private static bool IsSupportedUnderlyingType(Type type)
{
    if (Type.GetTypeCode(type) != TypeCode.Object || IsSupportedUnderlyingObjectType(type))
        return true;

    Type nullableUnderlying = Nullable.GetUnderlyingType(type);
    return nullableUnderlying != null && Type.GetTypeCode(nullableUnderlying) != TypeCode.Object;
} 

[Youssef1313]

Note:

The behavior today is already different between RDG and RDF in this case. RDG will already tolerate the empty string and use 'null' in this case.

aspnetcore/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/StaticRouteHandlerModel/Emitters/EndpointParameterEmitter.cs

Lines 149 to 152 in b761cb6

	codeWriter.WriteLine($"""else if (string.IsNullOrEmpty({temp_argument}))""");
	codeWriter.StartBlock();
	codeWriter.WriteLine($"""{output_argument} = {endpointParameter.DefaultValue};""");
	codeWriter.EndBlock();

In addition, MVC actually treats whitespace as null, not only empty string. But RDG only treats empty string as null.

Moreover, RDF itself on its own isn't consistent. If you create an endpoint with bool?[] query parameter, the empty string is tolerated in this case.