code: protected SortKey getSortKey(String column) {
  
          if (column == null) {
              return null;
          }
          if (column.equals(LIST_COLUMN_FULLNAME)) {
              return SortKey.fullName;
          } else if (column.equals(LIST_COLUMN_LOGIN)) {
              return SortKey.loginName;
          }
          return null;
      }
docs: Gets the sort key to use.<p>
  
  @param column the list column id
  @return the sort key