public function getDescriptor(string $classNamespace): ?Descriptor
    {
        if (!$this->isEmpty()) {
            /** @var Descriptor $descriptor */
            foreach ($this as $rootNamespace => $descriptor) {
                $rootNamespace = $descriptor->getRootNamespace();

                $doubleSlashed = str_replace('\\', '\\\\', $rootNamespace);
                $pattern = sprintf('|^%s\\.*|', $doubleSlashed);

                if (preg_match($pattern, $classNamespace)) {
                    return $descriptor;
                }
            }
        }

        return null;
    }