protected List<BoneLink> getBoneLinks() {
        assert boneLinkList != null;
        return boneLinkList;
    }
Access the list of bone links in a pre-order, depth-first traversal of
the link hierarchy.

@return the pre-existing list (not null)
jme3-jbullet/src/main/java/com/jme3/bullet/animation/DacLinks.java