code: protected SortKey getSortKey(String column) {
  
          if (column == null) {
              return null;
          }
          if (column.equals(LIST_COLUMN_EMAIL)) {
              return SortKey.email;
          } else if (column.equals(LIST_COLUMN_LOGIN)) {
              return SortKey.loginName;
          } else if (column.equals(LIST_COLUMN_NAME)) {
              return SortKey.fullName;
          }
          return null;
      }
docs: Returns the sort key for lazy list paging.<p>
  
  @param column the current column
  @return the sort key to use