Fixes: error in policy creation on contrail UI R3.0

When validating a value, check for None and if it is None, skip
validating it.

Change-Id: I3b4509e77528fe2fc2670eac195465e85d613426
Closes-Bug: 1577933

src/config/api-server/vnc_cfg_api_server.py

@@ -203,6 +203,8 @@ def _validate_complex_type(cls, dict_cls, dict_body):
             attr_type = attr_type_vals['attr_type']
             restrictions = attr_type_vals['restrictions']
             is_array = attr_type_vals.get('is_array', False)
+            if value is None:
+                continue
             if is_array:
                 if not isinstance(value, list):
                     raise ValueError('Field %s must be a list. Received value: %s'