optaplanner-benchmark/src/main/java/org/optaplanner/benchmark/impl/statistic/bestsolutionmutation/BestSolutionMutationSubSingleStatistic.java
@Override
    public void open(Solver<Solution_> solver) {
        InnerScoreDirectorFactory<Solution_> scoreDirectorFactory
                = (InnerScoreDirectorFactory<Solution_>) solver.getScoreDirectorFactory();
        SolutionDescriptor<Solution_> solutionDescriptor = scoreDirectorFactory.getSolutionDescriptor();
        listener.setMutationCounter(new MutationCounter<>(solutionDescriptor));
        solver.addEventListener(listener);
    }
@Override
    public void open(Solver<Solution_> solver) {
        InnerScoreDirectorFactory<Solution_> scoreDirectorFactory
                = (InnerScoreDirectorFactory<Solution_>) solver.getScoreDirectorFactory();
        SolutionDescriptor<Solution_> solutionDescriptor = scoreDirectorFactory.getSolutionDescriptor();
        listener.setMutationCounter(new MutationCounter<>(solutionDescriptor));
        solver.addEventListener(listener);
    }
************************************************************************