Hi, I am trying to add an UploadField to ModelAdmin, after the GridFieldList. But I always get an error " Call to a member function FormAction() on a non-object in ..../framework/forms/FormField.php on line 161". I can add TextField,DropdownField without any problems, but no luck with UploadField.
Did I miss something?

class MyExtension extends Extension{

    public static $has_one = array(
        'ImportCSV' => 'File'
    );

    public function updateEditForm($form){
        $fields = $form->Fields();

        $fields->push(
             new TextField('Title', 'Title')
        );//This one works

        $fields->push(
            new UploadField('ImportCSV', 'Import CSV')
        );//This one not working

    }
}