private function processStringPlaceholders($string, array $variables)
    {
        foreach ($variables as $key => $value) {
            if (!is_string($value) && !is_numeric($value) && !is_bool($value)) {
                continue;
            }

            $string = str_replace('{'.$key.'}', $value, (string) $string);
        }

        return $string;
    }