Jenkins Credentials not retained on plugin upgrade when underlying package is renamed

[vinita sanghi]

We are using Cloudbees plugin to extend Jenkins Credentials and include our own entry point. We renamed the package and now on a plugin upgrade the earlier credentials are not retained. Tried below:

//Retain backward compatibility
        @Initializer(before = InitMilestone.PLUGINS_STARTED)
        public static void createAliases() {        
            Items.XSTREAM2.addCompatibilityAlias("old class name", new name); 
}

Doesn't work