code: @Override
      public Double reduce(List<Double> values) {
          Double difference = values.get(0);
  
          for (int i = 1; i < values.size(); i++) {
              Double value = values.get(i);
  
              if (value == null) {
                  continue;
              }
              difference -= value;
          }
          return difference;
      }
docs: ~ Methods **************************************************************************************************************************************