Why is there such an error ?

2021-10-27 06:33:30,996+0800 INFO  (jsonrpc/3) [api.host] FINISH getStats error=<Fault 1: "<type 'exceptions.AttributeError'>:'NoneType' object has no attribute 'statistics'"> from=::ffff:10.200.211.80,48086 (api:52)

2021-10-27 06:33:30,997+0800 ERROR (jsonrpc/3) [jsonrpc.JsonRpcServer] Internal server error (__init__:350)

Traceback (most recent call last):

  File "/usr/lib/python2.7/site-packages/yajsonrpc/__init__.py", line 345, in _handle_request

    res = method(**params)

  File "/usr/lib/python2.7/site-packages/vdsm/rpc/Bridge.py", line 198, in _dynamicMethod

    result = fn(*methodArgs)

  File "<string>", line 2, in getStats

  File "/usr/lib/python2.7/site-packages/vdsm/common/api.py", line 50, in method

    ret = func(*args, **kwargs)

  File "/usr/lib/python2.7/site-packages/vdsm/API.py", line 1435, in getStats

    multipath=True)}

  File "/usr/lib/python2.7/site-packages/vdsm/host/api.py", line 77, in get_stats

    ret.update(cif.mom.getKsmStats())

  File "/usr/lib/python2.7/site-packages/vdsm/momIF.py", line 67, in getKsmStats

    stats = self._mom.getStatistics()['host']

  File "/usr/lib64/python2.7/xmlrpclib.py", line 1233, in __call__

    return self.__send(self.__name, args)

  File "/usr/lib64/python2.7/xmlrpclib.py", line 1591, in __request

    verbose=self.__verbose

  File "/usr/lib64/python2.7/xmlrpclib.py", line 1273, in request

    return self.single_request(host, handler, request_body, verbose)

  File "/usr/lib64/python2.7/xmlrpclib.py", line 1306, in single_request

    return self.parse_response(response)

  File "/usr/lib64/python2.7/xmlrpclib.py", line 1482, in parse_response

    return u.close()

  File "/usr/lib64/python2.7/xmlrpclib.py", line 794, in close

    raise Fault(**self._stack[0])

Fault: <Fault 1: "<type 'exceptions.AttributeError'>:'NoneType' object has no attribute 'statistics'">

2021-10-27 06:33:30,997+0800 INFO  (jsonrpc/3) [jsonrpc.JsonRpcServer] RPC call Host.getStats failed (error -32603) in 0.04 seconds (__init__:312)