docs: @SuppressWarnings("unchecked")
     public static <B> Class<? extends Builder<B>> builderForNonStrict(B built) {
        BuiltBy builtBy = built.getClass().getAnnotation(BuiltBy.class);
        if (builtBy == null) {
           return null;
        }
        return (Class<? extends Builder<B>>) builtBy.value();
     }