diff --git a/src/Ajax.php b/src/Ajax.php
index 07b1fbec92c..48457612c25 100644
--- a/src/Ajax.php
+++ b/src/Ajax.php
@@ -775,7 +775,7 @@ public static function updateItemJsCode(
 
                 $out .= $key . ":";
                 $regs = [];
-                if (!is_array($val) && preg_match('/^__VALUE(\d+)__$/', $val, $regs)) {
+                if (!is_array($val) && preg_match('/^__VALUE(\d+)__$/', $val ?? '', $regs)) {
                     $out .=  Html::jsGetElementbyID(Html::cleanId($toobserve[$regs[1]])) . ".val()";
                 } else if (!is_array($val) && $val === "__VALUE__") {
                     $out .=  Html::jsGetElementbyID(Html::cleanId($toobserve)) . ".val()";