--- a/src/pyams_portal/portlet.py	Wed Aug 25 14:12:34 2021 +0200
+++ b/src/pyams_portal/portlet.py	Wed Aug 25 17:27:31 2021 +0200
@@ -176,16 +176,20 @@
         result = super(PortletPreviewer, self).render()
         renderer = self.settings.get_renderer()
         translate = self.request.localizer.translate
-        result = PREVIEW_PREFIX.format(label=translate(_("Renderer:")),
-                                       renderer=translate(renderer.label)) + result
+        result = PREVIEW_PREFIX.format(
+            label=translate(_("Renderer:")),
+            renderer=translate(renderer.label if renderer is not None
+                               else _("!! MISSING RENDERER !!"))) + result
         return result
 
 
 PORTLETS_CACHE_REGION = 'portlets'
 PORTLETS_CACHE_NAME = 'PyAMS::portlet'
 
-PORTLETS_CACHE_KEY = 'portlet::{hostname}::{portlet}::{context}::{lang}'
-PORTLETS_CACHE_DISPLAY_CONTEXT_KEY = 'portlet::{hostname}::{portlet}::{context}::{display}::{lang}'
+PORTLETS_CACHE_KEY = 'portlet::{hostname}::{portlet}:' \
+                     ':{context}::{lang}'
+PORTLETS_CACHE_DISPLAY_CONTEXT_KEY = 'portlet::{hostname}::{portlet}:' \
+                                     ':{context}::{display}::{lang}'
 
 
 @implementer(IPortletRenderer)