docs: @Override
      public Set<IGroupMember> getChildren() throws GroupsException {
  
          final EntityIdentifier cacheKey = getUnderlyingEntityIdentifier();
          Element element = childrenCache.get(cacheKey);
  
          if (element == null) {
              final Set<IGroupMember> children = buildChildrenSet();
              element = new Element(cacheKey, children);
              childrenCache.put(element);
          }
  
          @SuppressWarnings("unchecked")
          final Set<IGroupMember> rslt = (Set<IGroupMember>) element.getObjectValue();
          return rslt;
      }