code: public void addPlugin(SimonConsolePlugin plugin) {
  		SimonConsolePlugin existingPlugin = getPluginById(plugin.getId());
  		if (existingPlugin != null) {
  			throw new IllegalArgumentException("Plugin " + plugin.getId() + " already registered");
  		}
  		plugins.add(plugin);
  	}
docs: Register a plugin
  
  @param plugin Plugin