--- a/cubicweb/web/action.py	Thu Dec 19 06:35:19 2019 +0100
+++ b/cubicweb/web/action.py	Thu Dec 19 06:35:54 2019 +0100
@@ -32,6 +32,7 @@
 Many examples are available in :mod:`cubicweb.web.views.actions`.
 """
 
+from typing import Optional
 
 from cubicweb import _
 
@@ -48,7 +49,7 @@
     __registry__ = 'actions'
     __select__ = match_search_state('normal')
     order = 99
-    category = 'moreactions'
+    category: Optional[str] = 'moreactions'
     # actions in category 'moreactions' can specify a sub-menu in which they should be filed
     submenu = None