Comment 4 for bug 1056122

For other attributes in XML content-type, if the value is null then '' is appended.
Eg:
In nova/api/ec2/cloud.py:CloudController._format_volume
<snip>
      if context.is_admin:
            # NOTE(dprince): project_id and host_id are unset w/ Cinder
            v['status'] = '%s (%s, %s, %s, %s)' % (
                volume['status'],
                volume.get('project_id', ''),
                volume.get('host', ''),
                instance_data,
                volume['mountpoint'])
<snip>