code: public void addSubmodule(final Module submodule) {
          if (!submodules.contains(submodule)) {
              submodule.setSubmodule(true);
  
              if (promoted) {
                  submodule.setPromoted(promoted);
              }
  
              submodules.add(submodule);
          }
      }
docs: Adds a submodule to the module.
  
  <P>
  INFO: If the module is promoted, all added submodule will be promoted.
  
  @param submodule Module