Failed to create cinder volume from glance image if description field for the image is empty

Issue

• Creating a cinder volume from an image fails with below error.

 # cinder create --display-name <VOL_NAME> --image-id <IMAGE_ID> <SIZE>
 ERROR: The server has either erred or is incapable of performing the requested operation. (HTTP 500) (Request-ID: req-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)

• Cinder api.log shows below error at the same time.

2015-10-07 08:47:25.556 4620 DEBUG taskflow.engines.action_engine.runner [req-f762d93c-67e7-4702-9fc1-4f82c5096fbf fdbf90ae7bc54fb487e23f53dff306c3 432c71216e3149f7ac182138758a6b85 - - -] Discarding failure 'Failure: ValueError: None is not of type u'string'

Failed validating u'type' in schema[u'additionalProperties']:
    {u'type': u'string'}

• The same kind of error will also happen if an instance is booted from this image.