code: private IRingSet getRingSetOfAtom(List ringSystems, IAtom atom) {
          IRingSet ringSetOfAtom = null;
          for (int i = 0; i < ringSystems.size(); i++) {
              if (((IRingSet) ringSystems.get(i)).contains(atom)) {
                  return (IRingSet) ringSystems.get(i);
              }
          }
          return ringSetOfAtom;
      }
docs: Gets the ringSetOfAtom attribute of the ModelBuilder3D object.
  
  @return              The ringSetOfAtom value