STC: NPE for raw type instanceof followed by parameterized extension method

Consider the following:

void test(... args) {
    args.each { object ->
        if (object instanceof Iterable) {
            object.each { test(it) }
        }
    }
}
test(1,[2,3])

The inferred type of "it" is causing NullPointerException at StaticTypeCheckingSupport.isAssignableTo(StaticTypeCheckingSupport.java:489)