+ /**
+ * Allows plugin managers to specify custom behavior if a plugin is not found.
+ *
+ * @param string $plugin_id
+ * The ID of the missing requested plugin.
+ * @param array $configuration
+ * An array of configuration relevant to the plugin instance.
+ *
+ * @return object
+ * A fallback plugin instance.
+ */
+ protected function handlePluginNotFound($plugin_id, array $configuration) {
+ $fallback_id = $this->getFallbackPluginId($plugin_id, $configuration);
+ return $this->getFactory()->createInstance($fallback_id, $configuration);
+ }
+