code: public List<Map<String, String>> pipelinePossibleStates(Assign action, List<Map<String, String>> possibleStateList) {
          for (Map<String, String> possibleState : possibleStateList) {
              possibleState.put(action.getName(), action.getExpr());
          }
  
          return possibleStateList;
      }
docs: Assigns one variable to one value
  
  @param action an Assign Action
  @param possibleStateList a current list of possible states produced so far from expanding a model state
  
  @return the same list, with every possible state augmented with an assigned variable, defined by action