DRL compilation error on a generic type property

public interface OrderLine<T extends Product> {
    T getProduct();
}

public interface Product {
    String getId();
    String getCategory();
}

// and I have concrete classes, ex. Book, BookOrderLine<Book>, DVD, DVDOrderLine<DVD>, ... etc

when
    $orderLine: OrderLine()

    // compilation failed
    Product(
        id == $orderLine.product.id || category == $orderLine.product.category
    ) from discountProducts

when
    $orderLine: OrderLine()

    // this is compiled, even if `Product(id == $orderLine.product.id)`
    Product(
        category == $orderLine.product.category
    ) from discountProducts