/**
  * Constructor
  *
  * Add a default initializer to ensure the plugin is valid after instance
  * creation.
  *
  * @param  null|ConfigInterface $configuration
  */
 public function __construct(ConfigInterface $configuration = null)
 {
     parent::__construct($configuration);
     $self = $this;
     $this->addInitializer(function ($instance) use($self) {
         if ($instance instanceof ServiceLocatorAwareInterface) {
             $instance->setServiceLocator($self);
         }
     });
 }