@Override
    public void removeInstancePort(String portId) {
        checkArgument(!Strings.isNullOrEmpty(portId), ERR_NULL_INSTANCE_PORT_ID);

        synchronized (this) {
            if (isInstancePortInUse(portId)) {
                final String error =
                            String.format(MSG_INSTANCE_PORT, portId, ERR_IN_USE);
                throw new IllegalStateException(error);
            }
            InstancePort instancePort = instancePortStore.removeInstancePort(portId);
            if (instancePort != null) {
                log.info(String.format(MSG_INSTANCE_PORT, instancePort.portId(), MSG_REMOVED));
            }
        }
    }
@Test(expected = IllegalArgumentException.class)
    public void testRemoveInstancePortWithNull() {
        target.removeInstancePort(null);
    }