minor fixes

filter_plugins/utils.py

@@ -46,6 +46,9 @@ class FilterModule(object):
     @staticmethod
     def ensure_list(data: (str, list)) -> list:
         # if user supplied a string instead of a list => convert it to match our expectations
+        if data is None:
+            return []
+
         if isinstance(data, list):
             return data