private function getPluginMiddleware($class)
    {
        if ($this->pluginMiddleware === null) {
            /** @noinspection PhpIncludeInspection */
            $this->pluginMiddleware = file_exists($this->pluginManifestOfMiddleware) ? include $this->pluginManifestOfMiddleware : [];
        }

        return isset($this->pluginMiddleware[$class]) && count($this->pluginMiddleware[$class]) == 1 ? $this->pluginMiddleware[$class][0] : null;
    }