audit-logger: use raw JSON with empty data to control unicode decode warnings.

Passing in empty dict triggers warnings on sqlalchemy level that we're trying to pass in NON unicode into Unicode column.

rhodecode/lib/audit_logger.py

@@ -21,6 +21,7 b''
 import logging
 import datetime
 
+from rhodecode.lib.jsonalchemy import JsonRaw
 from rhodecode.model import meta
 from rhodecode.model.db import User, UserLog, Repository
 
@@ -120,13 +121,13 b' def _store_log(action_name, action_data,'
     user_log.version = UserLog.VERSION_2
 
     user_log.action = action_name
-    user_log.action_data = action_data
+    user_log.action_data = action_data or JsonRaw(u'{}')
 
     user_log.user_ip = ip_address
 
     user_log.user_id = user_id
     user_log.username = username
-    user_log.user_data = user_data
+    user_log.user_data = user_data or JsonRaw(u'{}')
 
     user_log.repository_id = repository_id
     user_log.repository_name = repository_name