code: private void _addParameter(String parameterName, String parameterValue) {
          if (parameterName == null) {
              throw new NullPointerException("parameterName");
          }
          if (parameterValue == null) {
              throw new NullPointerException("parameterValue");
          }
          List<String> parameterValues = _getParameterValues(parameterName);
          parameterValues.add(parameterValue);
      }
docs: TODO: need to clean this up and provide some mix-in or other for param managment