code: public void addAttribute(StunAttribute attribute) throws IllegalArgumentException {
  		if (getAttributePresentity(attribute.getAttributeType()) == N_A) {
  			throw new IllegalArgumentException("The attribute " + attribute.getName() + " is not allowed in a " + getName());
  		}
  
  		synchronized (attributes) {
  			attributes.put(attribute.getAttributeType(), attribute);
  		}
  	}
docs: Adds the specified attribute to this message. If an attribute with that
  name was already added, it would be replaced.
  
  @param attribute
  the attribute to add to this message.
  
  @throws IllegalArgumentException
  if the message cannot contain such an attribute.