protected function whereNullHandler($key, string $prefix = '', string $operator = ''): IQueryBuilderHandler
    {
        $key = $this->adapterInstance->wrapSanitizer($this->addTablePrefix($key));
        $prefix = ($prefix !== '') ? $prefix . ' ' : $prefix;

        return $this->{$operator . 'Where'}($this->raw("$key IS {$prefix}NULL"));
    }