lbaas: update pool Error

the lbaas CMD:
1. frist create a pool
   $quantum lb-pool-create --lb-method ROUND_ROBIN --name mypool--protocol HTTP --subnet-id edad01a7-d616-4144-afb9-b8df941582c8

2. then update the pool
   $quantum lb-pool-update --request-format json mypool1 --name mypool

The Error info from the lbaas Agent:

013-05-30 14:12:59 ERROR [quantum.plugins.services.agent_loadbalancer.agent.manager] Unable to refresh device for pool: 1b9b9cc9-6510-4367-b729-c896db20f941
Traceback (most recent call last):
  File "/opt/stack/project/quantum/quantum/plugins/services/agent_loadbalancer/agent/manager.py", line 184, in refresh_device
    logical_config = self.plugin_rpc.get_logical_device(pool_id)
  File "/opt/stack/project/quantum/quantum/plugins/services/agent_loadbalancer/agent/api.py", line 47, in get_logical_device
    topic=self.topic
  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/proxy.py", line 86, in call
    return rpc.call(context, real_topic, msg, timeout)
  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/__init__.py", line 140, in call
    return _get_impl().call(CONF, context, topic, msg, timeout)
  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/impl_kombu.py", line 798, in call
    rpc_amqp.get_connection_pool(conf, Connection))
  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/amqp.py", line 615, in call
    rv = list(rv)
  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/amqp.py", line 564, in __iter__
    raise result
AttributeError: 'NoneType' object has no attribute 'status'
Traceback (most recent call last):

  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/amqp.py", line 433, in _process_data
    **args)

  File "/opt/stack/project/quantum/quantum/common/rpc.py", line 44, in dispatch
    quantum_ctxt, version, method, namespace, **kwargs)

  File "/opt/stack/project/quantum/quantum/openstack/common/rpc/dispatcher.py", line 148, in dispatch
    return getattr(proxyobj, method)(ctxt, **kwargs)

  File "/opt/stack/project/quantum/quantum/plugins/services/agent_loadbalancer/plugin.py", line 87, in get_logical_device
    or pool.vip.status != constants.ACTIVE):

AttributeError: 'NoneType' object has no attribute 'status'

       It is because that it has not check the existence of vip in a pool leading to the pool.vip.status to error