@Override
    public Set<Path> getPaths(ElementId src, ElementId dst) {
        return super.getPaths(src, dst, (LinkWeigher) null);
    }
@Test(expected = NullPointerException.class)
    public void testGetPathsWithNullSrc() {
        VirtualNetwork vnet = setupEmptyVnet();
        PathService pathService = manager.get(vnet.id(), PathService.class);
        pathService.getPaths(null, DID3);
    }