Index: openacs-4/packages/content-portlet/tcl/content-portlet-compare-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/content-portlet/tcl/content-portlet-compare-procs.tcl,v
diff -u -r1.5 -r1.6
--- openacs-4/packages/content-portlet/tcl/content-portlet-compare-procs.tcl	15 Aug 2018 16:43:08 -0000	1.5
+++ openacs-4/packages/content-portlet/tcl/content-portlet-compare-procs.tcl	12 Feb 2019 17:12:19 -0000	1.6
@@ -372,7 +372,7 @@
         set user_id [ad_conn user_id]
     }
     set description "New unit for content"
-    set parent_id [db_null]
+    set parent_id ""
     set unit_id [category::add -tree_id $tree_id \
 		     -parent_id $parent_id \
 		     -locale $language \