Index: openacs-4/packages/acs-tcl/tcl/site-nodes-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/site-nodes-procs.tcl,v
diff -u -r1.90.2.4 -r1.90.2.5
--- openacs-4/packages/acs-tcl/tcl/site-nodes-procs.tcl	10 Oct 2013 20:44:08 -0000	1.90.2.4
+++ openacs-4/packages/acs-tcl/tcl/site-nodes-procs.tcl	3 Sep 2014 19:32:28 -0000	1.90.2.5
@@ -250,11 +250,13 @@
     set package_id [get_object_id -node_id $node_id]
     set package_key [apm_package_key_from_id $package_id]
 
-    foreach inherited_package_key [nsv_get apm_package_inherit_order $package_key] {
-        apm_invoke_callback_proc \
-            -package_key $inherited_package_key \
-            -type before-unmount \
-            -arg_list [list package_id $package_id node_id $node_id]
+    if {[nsv_exists apm_package_inherit_order $package_key]} {
+        foreach inherited_package_key [nsv_get apm_package_inherit_order $package_key] {
+	    apm_invoke_callback_proc \
+		-package_key $inherited_package_key \
+		-type before-unmount \
+		-arg_list [list package_id $package_id node_id $node_id]
+	}
     }
 
     db_dml unmount_object {}