docs: public void addParameter(String paramName, String paramValue) 
      throws IllegalArgumentException {
          log.trace("enter PostMethod.addParameter(String, String)");
  
          if ((paramName == null) || (paramValue == null)) {
              throw new IllegalArgumentException(
                  "Arguments to addParameter(String, String) cannot be null");
          }
          super.clearRequestBody();
          this.params.add(new NameValuePair(paramName, paramValue));
      }