docs: public void addModifier(Modifier modifier) {
  		if (modifier != null) {
  			final String ruleName = modifier.getType();
  			if (!Strings.isEmpty(ruleName)) {
  				List<String> modifiers = this.modifiers.get(ruleName);
  				if (modifiers == null) {
  					modifiers = new ArrayList<>();
  					this.modifiers.put(ruleName, modifiers);
  				}
  				modifiers.addAll(modifier.getModifiers());
  			}
  		}
  	}