Index: openacs-4/packages/calendar-portlet/www/calendar-full-portlet.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/calendar-portlet/www/calendar-full-portlet.tcl,v
diff -u -r1.44.2.4 -r1.44.2.5
--- openacs-4/packages/calendar-portlet/www/calendar-full-portlet.tcl	13 Oct 2022 12:00:37 -0000	1.44.2.4
+++ openacs-4/packages/calendar-portlet/www/calendar-full-portlet.tcl	21 Mar 2023 17:41:54 -0000	1.44.2.5
@@ -68,7 +68,50 @@
 }
 
 set calendar_id [lindex $list_of_calendar_ids 0]
-db_0or1row select_calendar_package_id {select package_id from calendars where calendar_id=:calendar_id}
+
+#
+# Get the package_id of the calendar_id
+#
+if {$calendar_id == 0} {
+
+    #
+    # A calendar_id 0 may happen when showcasing the portal layout in
+    # "Portal Templates". This will be a dummy calendar portlet, so we
+    # deactivate the UI by disabling all links and buttons.
+    #
+    set package_id 0
+    set period_days [parameter::get -package_id $package_id -parameter ListView_DefaultPeriodDays -default 31]
+    template::add_body_handler -event load -script {
+        // Remove event listeners set on the mini-calendar
+        for (const day of document.querySelectorAll('[id^="mini-calendar-"]')) {
+            day.replaceWith(day.cloneNode(true));
+        }
+        // Disable all links
+        for (const link of document.querySelectorAll('[name="calendar"] ~ * a')) {
+            link.addEventListener('click', function (e) {
+                link.removeAttribute('href');
+            });
+        }
+        // Disable all buttons
+        for (const input of document.querySelectorAll('[name="calendar"] ~ * input, [name="calendar"] ~ * button')) {
+            input.disabled = true;
+        }
+    }
+
+} elseif {![db_0or1row select_calendar_package_id {
+    select package_id from calendars
+     where calendar_id = :calendar_id
+}]} {
+
+    #
+    # Could not find the supplied calendar_id, we complain in this
+    # case.
+    #
+    ad_log error "Invalid calendar_id in portlet configuration (calendar_id '$calendar_id')"
+    ad_return_complaint 1 "Invalid calendar_id in portlet configuration (calendar_id '$calendar_id')"
+    ad_script_abort
+}
+
 if { ![info exists period_days] } {
     if { [info exists community_id] && $community_id ne "" } {
         set period_days [parameter::get -package_id $package_id -parameter ListView_DefaultPeriodDays -default 31]