fix stan

Author: mvorisek

src/Table/Column/Flag.php

@@ -4,6 +4,7 @@
 
 namespace Atk4\Ui\Table\Column;
 
+use Atk4\Data\Field;
 use Atk4\Data\Model;
 use Atk4\Ui\Table;
 
@@ -18,7 +19,7 @@ class Flag extends Table\Column
     /** @var string|null Optional name of model field which contains country names. */
     public $name_field;
 
-    public function getHtmlTags(Model $row, $field)
+    public function getHtmlTags(Model $row, ?Field $field): array
     {
         $countryCode = $row->get($this->code_field);
         $countryName = $this->name_field ? $row->get($this->name_field) : null;