code: 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());
  		}
  	}
docs: Merges the contents of another property set into this; if this object and
  the other one both contain the same keys, those is the other object will
  override this object's.
  
  @param properties
  the other property set to merge into this (possibly overriding).
  @throws PropertiesException