code: public function init()
      {
          if (empty($this->controller)) {
              throw new InvalidConfigException('"controller" must be set.');
          }
  
          $controllers = [];
          foreach ((array) $this->controller as $urlName => $controller) {
              if (is_int($urlName)) {
                  $urlName = $this->pluralize ? Inflector::pluralize($controller) : $controller;
              }
              $controllers[$urlName] = $controller;
          }
          $this->controller = $controllers;
  
          $this->prefix = trim($this->prefix, '/');
  
          parent::init();
      }
docs: {@inheritdoc}