use symfony encode instead of json_encode

src/Tools/JsonSerializer.php

@@ -36,7 +36,8 @@ class JsonSerializer
     {
         $array = self::getInstance()->normalize($object);
         $arrayfiltered = self::array_filter_recursive($array, function($v){return $v !== null;});
-        $object = json_encode($arrayfiltered);
+        $jsonEncoder = new JsonEncoder();
+        $object = $jsonEncoder->encode($arrayfiltered, 'json');
         return $object;
     }