diff --git a/guix-data-service/model/derivation.scm b/guix-data-service/model/derivation.scm
index 24deffb..41c7c39 100644
--- a/guix-data-service/model/derivation.scm
+++ b/guix-data-service/model/derivation.scm
@@ -1702,13 +1702,14 @@ WHERE " criteria ";"))
      #t "debug: update-derivation-ids-hash-table!: lookup ~A file-names, ~A not cached\n"
      file-names-count (length missing-file-names))
 
-    (for-each
-     (match-lambda
-       ((id file-name)
-        (hash-set! derivation-ids-hash-table
-                   file-name
-                   (string->number id))))
-     (exec-query conn (select-existing-derivations missing-file-names)))))
+    (unless (null? missing-file-names)
+      (for-each
+       (match-lambda
+         ((id file-name)
+          (hash-set! derivation-ids-hash-table
+                     file-name
+                     (string->number id))))
+       (exec-query conn (select-existing-derivations missing-file-names))))))
 
 (define (derivation-file-names->derivation-ids conn derivation-file-names)
   (define (select-source-files-missing-nars derivation-ids)