diff --git a/src/db/CapacitorChannel.php b/src/db/CapacitorChannel.php
index 99676f4..a3d6297 100644
--- a/src/db/CapacitorChannel.php
+++ b/src/db/CapacitorChannel.php
@@ -233,8 +233,8 @@ class CapacitorChannel {
    *
    * cette méthode doit être utilisée dans {@link self::onUpdate()}
    */
-  function wasRowModified(array $values): bool {
-    return array_key_exists("modified_", $values);
+  function wasRowModified(array $values, array $pvalues): bool {
+    return $values["item__sum_"] !== $pvalues["item__sum_"];
   }
 
   final function serialize($item): ?string {
diff --git a/src/php/time/DateTime.php b/src/php/time/DateTime.php
index c978663..c73c968 100644
--- a/src/php/time/DateTime.php
+++ b/src/php/time/DateTime.php
@@ -139,6 +139,7 @@ class DateTime extends \DateTime {
   }
 
   function __construct($datetime="now", DateTimeZone $timezone=null) {
+    $datetime ??= "now";
     if ($datetime instanceof \DateTimeInterface) {
       if ($timezone === null) $timezone = $datetime->getTimezone();
       parent::__construct();