[OpenStack] keystone创建数据表问题

[SherkYoung]

在执行keystone-manage db_sync命令时出错：
ovs@fnic:~$ keystone-manage db_sync
Traceback (most recent call last):
File "/usr/bin/keystone-manage", line 28, in <module>
cli.main(argv=sys.argv, config_files=config_files)
File "/usr/lib/python2.7/dist-packages/keystone/cli.py", line 148, in main
return run(cmd, (args[:1] + args[2:]))
File "/usr/lib/python2.7/dist-packages/keystone/cli.py", line 134, in run
return CMDS[cmd](argv=args).run()
File "/usr/lib/python2.7/dist-packages/keystone/cli.py", line 36, in run
return self.main()
File "/usr/lib/python2.7/dist-packages/keystone/cli.py", line 55, in main
driver = utils.import_object(getattr(CONF, k).driver)
File "/usr/lib/python2.7/dist-packages/keystone/common/utils.py", line 60, in import_object
__import__(import_str)
TypeError: __import__() argument 1 must be string, not None

请问这个问题该如何解决啊？