Use empty string as default value for Security Group description

* Return SG description field to empty string if none value.

Change-Id: Ic40c614b3bafbd93e50569d4c31fcfb584954e7a
Closes-Bug: #1766508
(cherry picked from commit e5e4322)

src/config/vnc_openstack/vnc_openstack/neutron_plugin_db.py

@@ -1144,7 +1144,10 @@ def _security_group_vnc_to_neutron(self, sg_obj, memo_req=None, oper=READ):
         else:
             sg_q_dict['name'] = sg_obj.display_name
 
+        # If description is not specified by the user, assign empty string
         sg_q_dict['description'] = sg_obj.get_id_perms().get_description()
+        if not sg_q_dict['description']:
+            sg_q_dict['description'] = ""
 
         # get security group rules
         sg_q_dict['security_group_rules'] = []
@@ -1164,6 +1167,7 @@ def _security_group_vnc_to_neutron(self, sg_obj, memo_req=None, oper=READ):
     def _security_group_neutron_to_vnc(self, sg_q, oper):
         if oper == CREATE:
             project_obj = self._get_project_obj(sg_q)
+
             id_perms = IdPermsType(enable=True,
                                    description=sg_q.get('description'))
             sg_vnc = SecurityGroup(name=sg_q['name'],