[Validator] added magic method __isset() to File Constraint class

src/Symfony/Component/Validator/Constraints/File.php

@@ -88,6 +88,15 @@ class File extends Constraint
         return parent::__get($option);
     }
 
+    public function __isset($option)
+    {
+        if ('maxSize' === $option) {
+            return true;
+        }
+
+        return parent::__isset($option);
+    }
+
     private function normalizeBinaryFormat($maxSize)
     {
         $sizeInt = (int) $maxSize;