code: public String getMessage() {
          if (performanceDataList.isEmpty()) {
              return messageString;
          }
          StringBuilder res = new StringBuilder(messageString).append('|');
          for (PerformanceData pd : performanceDataList) {
              res.append(pd.toPerformanceString()).append(' ');
          }
          return res.toString();
      }
docs: Returns the message. If the performance data has been passed in, they are
  attached at the end of the message accordingly to the Nagios
  specifications
  
  
  @return The message and optionally the performance data