code: private void putRestrictedAttributes(Map<String, String> attributes) {
  
          // Set disabled attribute
          attributes.put(DISABLED_ATTRIBUTE_NAME, getModel().isDisabled() ? "true" : null);
  
      }
docs: Stores all restricted (privileged) attributes within the given Map,
  pulling the values of those attributes from the underlying user group
  model. If no value is yet defined for an attribute, that attribute will
  be set to null.
  
  @param attributes
  The Map to store all restricted attributes within.