public static function render_all($user_id)
 {
     $fields = WJ_FieldUser::get_all($user_id);
     if (isset($fields)) {
         $output = '';
         foreach ($fields as $field) {
             $field_render = new self($field);
             $output .= '<tr>' . '<th scope="row">' . $field_render->label() . '</th><td>' . $field_render->input() . '</td></tr>';
         }
         return $output;
     } else {
         return null;
     }
 }