code: private static void checkTransition(Map<Transition, Collection<TileRef>> transitions,
                                          MapTransitionExtractor extractor,
                                          Tile tile)
      {
          final Transition transition = extractor.getTransition(tile);
          if (transition != null)
          {
              getTiles(transitions, transition).add(new TileRef(tile));
  
              final Transition symetric = new Transition(transition.getType().getSymetric(),
                                                         transition.getOut(),
                                                         transition.getIn());
              getTiles(transitions, symetric).add(new TileRef(tile));
          }
      }
docs: Check the tile transition and add it to transitions collection if valid.
  
  @param transitions The transitions collection.
  @param extractor The transition extractor.
  @param tile The tile to check.