docs: public static JRDesignExpression getParameterExpression(Subreport sr) {
          JRDesignExpression exp = new JRDesignExpression();
          exp.setValueClassName(java.util.Map.class.getName());
          if (sr.isUseParentReportParameters()) {
              exp.setText(REPORT_PARAMETERS_MAP);
              return exp;
          }
  
          if (sr.getParametersExpression() == null)
              return null;
  
          if (sr.getParametersMapOrigin() == DJConstants.SUBREPORT_PARAMETER_MAP_ORIGIN_PARAMETER) {
              exp.setText(REPORT_PARAMETERS_MAP + ".get( \"" + sr.getParametersExpression() + "\" )");
              return exp;
          }
  
          if (sr.getParametersMapOrigin() == DJConstants.SUBREPORT_PARAMETER_MAP_ORIGIN_FIELD) {
              exp.setText("$F{" + sr.getParametersExpression() + "}");
              return exp;
          }
  
          return null;
      }