Add missing Event class cache invalidation

Needed when calling the refresh() method. Otherwise
null StoredEvent instances will be returned.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -16,6 +16,8 @@
 - Fix NamedMultiWidget issue on Python 3. Affects
   document checkout form. GitLab issue #683. Thanks
   to John Bentley (@johnbentleyii) for the report.
+- Add missing Event class cache invalidation when
+  calling the refresh() method.
 
 3.2.9 (2019-11-03)
 ==================

mayan/apps/events/classes.py

@@ -73,6 +73,9 @@ class EventType(object):
     @classmethod
     def refresh(cls):
         for event_type in cls.all():
+            # Invalidate cache and recreate store events while repopulating
+            # cache
+            event_type.stored_event_type = None
             event_type.get_stored_event_type()
 
     def __init__(self, namespace, name, label):