@Override
    public Set<Link> getEgressLinks(ConnectPoint connectPoint) {
        checkNotNull(connectPoint, CONNECT_POINT_NULL);
        return manager.getVirtualLinks(this.networkId())
                .stream()
                .filter(link -> (connectPoint.equals(link.dst())))
                .collect(Collectors.toSet());
    }
@Test(expected = NullPointerException.class)
    public void testGetEgressLinksByNullId() {
        manager.registerTenantId(TenantId.tenantId(tenantIdValue1));
        VirtualNetwork virtualNetwork = manager.createVirtualNetwork(TenantId.tenantId(tenantIdValue1));
        LinkService linkService = manager.get(virtualNetwork.id(), LinkService.class);

        // test the getEgressLinks() method with a null connect point.
        linkService.getEgressLinks(null);
    }