private function loadFile(
        array &$items,
        string $path,
        string $pathRelative,
        string $configKey,
        $environment = null
    ): void {
        // Build filename.
        $filename = $path;
        if ($pathRelative !== null && $pathRelative !== '') {
            $filename .= '/' . $pathRelative;
        }
        $filename .= '/' . $configKey;
        if ($environment !== null) {
            $filename .= '.' . (string)$environment;
        }
        $filename .= '.php';

        // Load configuration.
        if (!file_exists($filename)) {
            return;
        }
        $config = require($filename);

        // Parse config.
        $itemsData = &$items;
        if ($pathRelative !== '') {
            $pathSegments = explode('.', $pathRelative);
            foreach ($pathSegments as $pathSegment) {
                $itemsData = &$itemsData[$pathSegment];
            }
        }
        if (!isset($itemsData[$configKey])) {
            $itemsData[$configKey] = null;
        }
        if (is_array($itemsData[$configKey]) && is_array($config)) {
            $itemsData[$configKey] = array_merge($itemsData[$configKey], $config);
        } else {
            $itemsData[$configKey] = $config;
        }
    }