diff --git a/include/class_templateHandling.inc b/include/class_templateHandling.inc
index 72867713fa3c9eb68ce41084d0d04635cb7d59a7..f8823b50108bba49d3f50b8ad3761cb0fc529a85 100644
--- a/include/class_templateHandling.inc
+++ b/include/class_templateHandling.inc
@@ -436,6 +436,9 @@ class templateHandling
       $args[] = 1;
     }
     $numberGenerator = function ($mandatory, $start, $step) {
+      if (!$mandatory) {
+        yield '';
+      }
       $i = $start;
       while (TRUE) {
         yield $i;