docs: @Override
    public List<IntegerSolution> execute(List<IntegerSolution> solutions) {
      if (null == solutions) {
        throw new JMetalException("Null parameter") ;
      } else if (solutions.size() != 2) {
        throw new JMetalException("There must be two parents instead of " + solutions.size()) ;
      }
  
      return doCrossover(crossoverProbability, solutions.get(0), solutions.get(1)) ;
    }