code: public List<? extends Solution<?>> normalize(List<? extends Solution<?>> solutionList) {
      Front normalizedFront ;
      if (solutionList == null) {
        throw new JMetalException("The front is null") ;
      }
  
      normalizedFront = getNormalizedFront(new ArrayFront(solutionList), maximumValues, minimumValues);
  
      return FrontUtils.convertFrontToSolutionList(normalizedFront) ;
    }
docs: Returns a normalized front
  @param solutionList
  @return