code: public Map getQueryParamsForPreviousPage() {
          Map params = _codec.getExistingParams();
          Map newParams = new HashMap();
  
          PagerModel pagerModel = getDataGridState().getPagerModel();
          assert pagerModel != null;
  
          addSortParams(newParams);
          addFilterParams(newParams);
          newParams.putAll(_codec.buildPageParamMap(new Integer(pagerModel.getRowForPreviousPage()),
                                                    new Integer(pagerModel.getPageSize())));
  
          params = mergeMaps(params, newParams);
          params = transformMap(params);
  
          return params;
      }
docs: <p>
  Get a URL query parameter map that will change the data grid's page value to display the
  <i>previous</i> page in a data set relative to the current page.  This map also contains all of
  the other existing URL parameters.  The {@link Map} contains key / value pairs of type
  String / String[].
  </p>
  @return the URL and data grid state needed to change to the <i>previous</i> page for a data grid