Class properties inherit from an abstract class recognized with type "object"

[gabry]

Hi,
in my controllers each filter of GET methods is defined as a complex class.
Each property of the complex class (e.g. ProductFilter) inherits from an abstract class.
Here https://github.com/gabry/GZWebApplication.git replicated code in order to allow help me troubleshooting.
I expected to fill on Swagger UI each property of Product filter, actually they're seen as an "object".

Read here https://github.com/RicoSuter/NJsonSchema/wiki/Inheritance, added attributes over classes, but the properties FilterId, Name, Category, Price result as an "object".
Read some other issues, but none of them allow me to solve the issue:
RicoSuter/NSwag#1652
#829

Can you please help me?

Thanks.
Regards

public IHttpActionResult GetProductByComplexFilter([FromUri] ProductFilter filter)

public class ProductFilter {
public GZIntFilter FilterId { get; set; }
public GZStringFilter Name { get; set; }
public GZStringFilter Category { get; set; }
public GZIntFilter Price { get; set; }
}

public class GZStringFilter : GZFilter {
//...
}

public class GZIntFilter : GZFilter<int?> {
//...
}

public abstract class GZFilter : IGZFilter {
//...
}

public interface IGZFilter {
bool IsValid { get; }
}