can't retrieve resource details in v2-api

Using the ceilometer-api-v2, when accessing the URL of "http://localhost:8777/v2/resources/7139fe36-ebf7-461a-b095-e81a312349fe/",

 the following error returned in browser:

error_message: "{"debuginfo": null, "faultcode": "Server", "faultstring": "'generator' object has no attribute '__getitem__'"}"

The ceilometer-api-v2 dumps the following exception info:

2013-02-08 12:42:09,511 ERROR [wsme.api][MainThread] Server-side error: "'generator' object has no attribute '__getitem__'". Detail:
Traceback (most recent call last):

  File "/usr/local/lib/python2.7/dist-packages/WSME-0.5b1-py2.7.egg/wsmeext/pecan.py", line 68, in callfunction
    result = f(self, *args, **kwargs)

  File "/opt/stack/ceilometer/ceilometer/api/controllers/v2.py", line 489, in get_one
    r = request.storage_conn.get_resources(resource=resource_id)[0]

TypeError: 'generator' object has no attribute '__getitem__'

localhost - - [08/Feb/2013 12:42:09] "GET /v2/resources/7139fe36-ebf7-461a-b095-e81a312349fe/ HTTP/1.1" 500 141