swift proxy start error

Traceback (most recent call last):
  File "/usr/bin/swift-proxy-server", line 22, in <module>
    run_wsgi(conf_file, 'proxy-server', default_port=8080, **options)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 122, in run_wsgi
    loadapp('config:%s' % conf_file, global_conf={'log_name': log_name})
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 247, in loadapp
    return loadobj(APP, uri, name=name, **kw)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 272, in loadobj
    return context.create()
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 710, in create
    return self.object_type.invoke(self)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 207, in invoke
    app = filter(app)
  File "/usr/lib/python2.7/dist-packages/keystone/middleware/auth_token.py", line 347, in auth_filter
    return AuthProtocol(app, conf)
  File "/usr/lib/python2.7/dist-packages/keystone/middleware/auth_token.py", line 119, in __init__
    self._init_protocol_common(app, conf)  # Applies to all protocols
  File "/usr/lib/python2.7/dist-packages/keystone/middleware/auth_token.py", line 85, in _init_protocol_common
    self.service_port = int(conf.get('service_port'))
TypeError: int() argument must be a string or a number, not 'NoneType'