Comment 6 for bug 1064835

So does the following fix this issue?

--- a/keystoneclient/shell.py
+++ b/keystoneclient/shell.py
@@ -131,7 +131,7 @@ class OpenStackIdentityShell(object):

         parser.add_argument('--os-cacert',
                             metavar='<ca-certificate>',
- default=env('OS_CA_CERT'),
+ default=env('OS_CA_CERT', default=None),
                             help='Defaults to env[OS_CACERT]')
         parser.add_argument('--os_cacert',
                             help=argparse.SUPPRESS)

or more generic:

--- a/keystoneclient/shell.py
+++ b/keystoneclient/shell.py
@@ -42,7 +42,7 @@ def env(*vars, **kwargs):
         value = os.environ.get(v, None)
         if value:
             return value
- return kwargs.get('default', '')
+ return kwargs.get('default', None)

 class OpenStackIdentityShell(object):