addClass with DefaultPackage opens addPackage to null arguments

When adding a Class in addClass, we do a addPackage with a Filter to match inner classes of that class.

When adding a Class in Default package, the Package we padd to addPackage is null. Meaning addPackage can't verify non null values.

The downside is, if someone happens to add, e.g.
addPakcage(true, Package.get("some-missing-package")), addPackage will be called with null, and null means /, which means all found packages are added.

We need to split addPackage(boolean, Filter, Package...) into two methods, one external which does the null checks from the user and one internal that does not check for null(to support Class in default package).