@Override
    public boolean isLatest(Topology topology) {
        Topology currentTopology = currentTopology();
        return defaultTopology(topology).getGraph()
                .equals(defaultTopology(currentTopology).getGraph());
    }
@Test(expected = NullPointerException.class)
    public void testIsLatestByNullTopology() {
        manager.registerTenantId(TenantId.tenantId(tenantIdValue1));
        VirtualNetwork virtualNetwork = manager.createVirtualNetwork(TenantId.tenantId(tenantIdValue1));
        TopologyService topologyService = manager.get(virtualNetwork.id(), TopologyService.class);

        // test the isLatest() method with a null topology.
        topologyService.isLatest(null);
    }