class BlockPluginCollection

class BlockPluginCollection extends DefaultSingleLazyPluginCollection {
    
    /**
     * The block ID this plugin collection belongs to.
     *
     * @var string
     */
    protected $blockId;
    
    /**
     * Constructs a new BlockPluginCollection.
     *
     * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
     *   The manager to be used for instantiating plugins.
     * @param string $instance_id
     *   The ID of the plugin instance.
     * @param array $configuration
     *   An array of configuration.
     * @param string $block_id
     *   The unique ID of the block entity using this plugin.
     */
    public function __construct(PluginManagerInterface $manager, $instance_id, array $configuration, $block_id) {
        parent::__construct($manager, $instance_id, $configuration);
        $this->blockId = $block_id;
    }
    
    /**
     * {@inheritdoc}
     *
     * @return \Drupal\Core\Block\BlockPluginInterface
     */
    public function &get($instance_id) {
        return parent::get($instance_id);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function initializePlugin($instance_id) {
        if (!$instance_id) {
            throw new PluginException("The block '{$this->blockId}' did not specify a plugin.");
        }
        try {
            parent::initializePlugin($instance_id);
        } catch (PluginException $e) {
            $module = $this->configuration['provider'];
            // Ignore blocks belonging to uninstalled modules, but re-throw valid
            // exceptions when the module is installed and the plugin is
            // misconfigured.
            if (!$module || \Drupal::moduleHandler()->moduleExists($module)) {
                throw $e;
            }
        }
    }

}