Index: openacs-4/packages/categories/tcl/category-trees-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/categories/tcl/category-trees-procs.tcl,v
diff -u -r1.31.2.8 -r1.31.2.9
--- openacs-4/packages/categories/tcl/category-trees-procs.tcl	26 Apr 2019 13:31:22 -0000	1.31.2.8
+++ openacs-4/packages/categories/tcl/category-trees-procs.tcl	26 Apr 2019 13:34:13 -0000	1.31.2.9
@@ -391,7 +391,10 @@
         Reloads all category tree hierarchies in the cache.
         @author Timo Hentschel (timo@timohentschel.de)
     } {
-        catch {nsv_unset category_trees}
+        if {[nsv_names category_trees] ne ""} {
+            nsv_unset category_trees
+        }
+
         set tree_id_old 0
         set cur_level 1
         set stack [list]