diff --git a/lib-sql/functions/utils.sql b/lib-sql/functions/utils.sql
index 3baf8240..30a2aa8a 100644
--- a/lib-sql/functions/utils.sql
+++ b/lib-sql/functions/utils.sql
@@ -2,7 +2,7 @@
 --
 -- This file is part of Nominatim. (https://nominatim.org)
 --
--- Copyright (C) 2025 by the Nominatim developer community.
+-- Copyright (C) 2026 by the Nominatim developer community.
 -- For a full list of authors see the git log.
 
 -- Assorted helper functions for the triggers.
@@ -46,13 +46,13 @@ DECLARE
   r INTEGER[];
 BEGIN
   IF array_upper(a, 1) IS NULL THEN
-    RETURN b;
+    RETURN COALESCE(b, '{}'::INTEGER[]);
   END IF;
   IF array_upper(b, 1) IS NULL THEN
-    RETURN a;
+    RETURN COALESCE(a, '{}'::INTEGER[]);
   END IF;
   r := a;
-  FOR i IN 1..array_upper(b, 1) LOOP  
+  FOR i IN 1..array_upper(b, 1) LOOP
     IF NOT (ARRAY[b[i]] <@ r) THEN
       r := r || b[i];
     END IF;