TMSS-2576: set referer and csrftoken in tmss_http_rest_client.py requests

SAS/TMSS/client/lib/tmss_http_rest_client.py

@@ -188,6 +188,8 @@ class TMSSsession(object):
             request_method = self.session.options
 
         if 'csrftoken' in self.session.cookies:
+            if headers is None:
+                headers = dict()
             headers.update({'Referer': self.host_url, 'X-CSRFToken': self.session.cookies['csrftoken']})
 
         for attempt_nr in range(attempt_count):