docs: public void merge(Properties properties) throws PropertiesException {
  		if(isLocked()) {
  			throw new PropertiesException("properties map is locked, its contents cannot be altered.");
  		}				
  		assert properties != null;
  		for(Entry<String, String> entry : properties.entrySet()) {
  			this.put(entry.getKey(), entry.getValue());
  		}
  	}