code: private boolean parameterExists() {
          parameterValue = pageContext.getAttribute(parameterName, PageContext.REQUEST_SCOPE);
  
          // -- Harald K 20020726
          if (parameterValue == null) {
              parameterValue = pageContext.getRequest().getParameter(parameterName);
          }
  
          return (parameterValue != null);
      }
docs: This method is used to determine whether the parameter whose name is
  stored in {@code mParameterName} exists within the {@code
  PageContext.REQUEST_SCOPE} scope.  If the parameter does exist,
  then this method will return {@code true}, otherwise it returns
  {@code false}.  This method has the side affect of loading the
  parameter value into {@code mParameterValue} if the parameter
  does exist.
  
  @return {@code true} if the parameter whose name is in {@code
  mParameterName} exists in the {@code PageContext.REQUEST_SCOPE
  } scope, {@code false} otherwise.