code: public List<IntVar> getIncoming(Node n) {
          List<IntVar> l = incoming.get(n);
          if (l == null) {
              l = Collections.emptyList();
          }
          return l;
      }
docs: Get the start moment of the movements that terminate
  on a given node
  
  @param n the destination node
  @return a list of start moment. May be empty