code: SortedSet<ModuleElement> getModuleList(Map<String, SortedSet<ModuleElement>> map,
              String groupname) {
          return map.computeIfAbsent(groupname, g -> new TreeSet<>(configuration.utils.makeModuleComparator()));
      }
docs: For the given group name, return the module list, on which it is mapped.
  Create a new list, if not found.
  
  @param map Map to be searched for group name.
  @param groupname Group name to search.