code: @Nullable
      private Comparator<SimpleItem> getComparator() {
          switch (sortingStrategy) {
              case SORT_ASCENDING:
                  return new AlphabetComparatorAscending();
              case SORT_DESCENDING:
                  return new AlphabetComparatorDescending();
              case SORT_NONE:
                  return null;
          }
  
          throw new RuntimeException("This sortingStrategy is not supported.");
      }
docs: Returns the appropriate Comparator for the current sorting strategy or null if no strategy is
  set. (SORT_NONE)
  
  @return The comparator or null.