docs: public void addParameter(String pName, Object pValue) {
          // Check that we haven't already saved this parameter
          if (!parameterNames.contains(pName)) {
              parameterNames.add(pName);
  
              // Now check if this parameter already exists in the page.
              Object obj = getRequest().getAttribute(pName);
              if (obj != null) {
                  oldParameters.put(pName, obj);
              }
          }
  
          // Finally, insert the parameter in the request scope.
          getRequest().setAttribute(pName, pValue);
      }