code: public function init()
      {
          if ($this->controllerNamespace === null) {
              $class = get_class($this);
              if (($pos = strrpos($class, '\\')) !== false) {
                  $this->controllerNamespace = substr($class, 0, $pos) . '\\controllers';
              }
          }
      }
docs: Initializes the module.
  
  This method is called after the module is created and initialized with property values
  given in configuration. The default implementation will initialize [[controllerNamespace]]
  if it is not set.
  
  If you override this method, please make sure you call the parent implementation.