code: public void addAttributeValue(String attributeName, String value) {
  
          if (m_entityAttributes.containsKey(attributeName)) {
              throw new RuntimeException("Attribute already exists with a entity type value.");
          }
          if (m_simpleAttributes.containsKey(attributeName)) {
              m_simpleAttributes.get(attributeName).add(value);
          } else {
              List<String> values = new ArrayList<String>();
              values.add(value);
              m_simpleAttributes.put(attributeName, values);
          }
          fireChange();
      }
docs: Adds the given attribute value.<p>
  
  @param attributeName the attribute name
  @param value the attribute value