diff --git a/opengever/sharing/local_roles_lookup/manager.py b/opengever/sharing/local_roles_lookup/manager.py
index a390ce5694..a064966c16 100644
--- a/opengever/sharing/local_roles_lookup/manager.py
+++ b/opengever/sharing/local_roles_lookup/manager.py
@@ -69,6 +69,11 @@ def update_lookup_table(self, context):
         self.delete_all_by_uid(context.UID())
 
         for principal, roles in context.get_local_roles():
+            if not principal:
+                # It's possible that some local roles are assigned to 'None'.
+                # We should skip those principals.
+                continue
+
             managed_roles = list(set(roles).intersection(self.MANAGED_ROLES))
             if not managed_roles:
                 continue