@Override
    public List<PortStatistics> getPortStatistics(DeviceId deviceId) {
        checkNotNull(deviceId, DEVICE_NULL);
        // TODO not supported at the moment.
        return ImmutableList.of();
    }
@Test(expected = NullPointerException.class)
    public void testGetPortsStatisticsByNullId() {
        manager.registerTenantId(TenantId.tenantId(tenantIdValue1));
        VirtualNetwork virtualNetwork = manager.createVirtualNetwork(TenantId.tenantId(tenantIdValue1));
        DeviceService deviceService = manager.get(virtualNetwork.id(), DeviceService.class);

        // test the getPortStatistics() method using a null device identifier
        deviceService.getPortStatistics(null);
    }