code: public static <S> UnweightedNode<Void,S> newNodeWithoutAction(UnweightedNode<Void,S> previousNode, S state){
          return new UnweightedNode<Void, S>(previousNode, state, null);
      }
docs: This static method creates an unweighted node without defining an explicit action, using
  the parent node and a state.
  
  @param previousNode parent node
  @param state state of the node to be created
  @param <S> type of the state
  @return new node for the state specified, without need of specifying the action connecting them