public function isThemePackage($packageName)
    {
        $composerPackage = $this->findPackageGlobal($packageName);

        if (is_null($composerPackage) === true) {
            throw new \RuntimeException(sprintf('The theme: "%s" does not exist.', $packageName));
        }

        return $composerPackage->getType() == self::PACKAGE_TYPE_THEME;
    }