python - RPC が AttributeError: 'NoneType' object has no attribute 'call' でクラッシュする

Question

platform.historian をクエリするエージェントを開発しようとしていますが、RPC クエリ メソッドを使用すると次のエラー メッセージが表示されます: AttributeError: 'NoneType' object has no attribute 'call'

class TCMAgent(Agent):
    def __init__(self, config_path, **kwargs):
        super(TCMAgent, self).__init__(**kwargs)
        self.config = utils.load_config(config_path)
        self.site = self.config.get('campus')
        self.building = self.config.get('building')
        self.unit = self.config.get('unit')
        self.subdevices = self.config.get('subdevices')
        self.subdevice = self.subdevices[0]
    ...
    ...


def test_api():
    '''To test Volttron APIs'''
    import os

    topic_tmpl = "{campus}/{building}/{unit}/{subdevice}/{point}"
    tcm = TCMAgent(os.environ.get('AGENT_CONFIG'))

    topic1 = topic_tmpl.format(campus='PNNL',
                               building='SEB',
                               unit='AHU1',
                               subdevice='VAV123A',
                               point='MaximumZoneAirFlow')
    result = tcm.vip.rpc.call('platform.historian',
                              'query',
                              topic=topic1,
                              count=20,
                              order="LAST_TO_FIRST").get(timeout=100)
    assert result is not None

if __name__ == '__main__':
    # Entry point for script
    #sys.exit(main())
    test_api()

以下のエラー トレースを更新します。

2016-07-19 14:58:31,362 volttron.platform.vip.agent.core DEBUG: publickey is None
2016-07-19 14:58:31,362 volttron.platform.vip.agent.core DEBUG: secretkey is None
Traceback (most recent call last):
  File "/home/hngo/volttron/examples/TCMAgent/tcm/agent.py", line 236, in <module>
    test_api()
  File "/home/hngo/volttron/examples/TCMAgent/tcm/agent.py", line 230, in test_api
    order="LAST_TO_FIRST").get(timeout=100)
  File "/home/hngo/volttron/volttron/platform/vip/agent/subsystems/rpc.py", line 303, in call
    request, result = self._dispatcher.call(method, args, kwargs)
AttributeError: 'NoneType' object has no attribute 'call'