docs: public void addLoadedExtension(Extension extension) {
  		if (extension == null) {
  			throw new IllegalArgumentException("Parameter extension must not be null.");
  		}
  
  		if (loadedExtensions == null) {
  			loadedExtensions = new ArrayList<>(1);
  		}
  
  		if (!loadedExtensions.contains(extension)) {
  			loadedExtensions.add(extension);
  			extension.setAddOn(this);
  		}
  	}