diff --git a/tackerclient/tacker/v1_0/nfvo/vim_utils.py b/tackerclient/tacker/v1_0/nfvo/vim_utils.py
index 2a68632d..99bdfa26 100644
--- a/tackerclient/tacker/v1_0/nfvo/vim_utils.py
+++ b/tackerclient/tacker/v1_0/nfvo/vim_utils.py
@@ -74,16 +74,9 @@ def args2body_vim(config_param, vim):
                 message='username and password or bearer_token must be'
                         'provided',
                 status_code=404)
-        if 'ssl_ca_cert' in config_param:
-            ssl_ca_cert = config_param.pop('ssl_ca_cert', '')
-            if ssl_ca_cert == 'None':
-                vim['auth_cred']['ssl_ca_cert'] = None
-            else:
-                vim['auth_cred']['ssl_ca_cert'] = ssl_ca_cert
-        else:
-            raise exceptions.TackerClientException(
-                message='ssl_ca_cert must be provided or leave it with None',
-                status_code=404)
+        ssl_ca_cert = config_param.pop('ssl_ca_cert', '')
+        if ssl_ca_cert:
+            vim['auth_cred']['ssl_ca_cert'] = ssl_ca_cert
 
 
 def validate_auth_url(url):
diff --git a/tackerclient/tests/unit/vm/test_cli10_vim_k8s_with_bearer_token.py b/tackerclient/tests/unit/vm/test_cli10_vim_k8s_with_bearer_token.py
index 96ac09af..fe14ea37 100644
--- a/tackerclient/tests/unit/vm/test_cli10_vim_k8s_with_bearer_token.py
+++ b/tackerclient/tests/unit/vm/test_cli10_vim_k8s_with_bearer_token.py
@@ -35,7 +35,7 @@ class CLITestV10VIMJSON(test_cli10.CLITestV10Base):
         plurals = {'vims': 'vim'}
         super(CLITestV10VIMJSON, self).setUp(plurals=plurals)
         self.vim_project = {'name': 'default'}
-        self.auth_cred = {'bearer_token': 'xyz', 'ssl_ca_cert': None}
+        self.auth_cred = {'bearer_token': 'xyz', 'ssl_ca_cert': "None"}
         self.auth_url = 'https://1.2.3.4:6443'
         self.type = 'kubernetes'
 
diff --git a/tackerclient/tests/unit/vm/test_vim_utils.py b/tackerclient/tests/unit/vm/test_vim_utils.py
index 11b3c82a..3f0df3f5 100644
--- a/tackerclient/tests/unit/vm/test_vim_utils.py
+++ b/tackerclient/tests/unit/vm/test_vim_utils.py
@@ -63,7 +63,7 @@ class TestVIMUtils(testtools.TestCase):
 
     def test_args2body_kubernetes_vim_bearer(self):
         config_param = {'bearer_token': sentinel.bearer_token,
-                        'ssl_ca_cert': None,
+                        'ssl_ca_cert': "None",
                         'project_name': sentinel.prj_name,
                         'type': 'kubernetes'}
         vim = {}
diff --git a/tox.ini b/tox.ini
index 9722f0b0..add34820 100644
--- a/tox.ini
+++ b/tox.ini
@@ -37,3 +37,6 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 ignore = E125
 show-source = true
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
+# F821 undefined name 'unicode'
+# if isinstance(config, str) or isinstance(config, unicode):
+builtins = unicode