code: private static String lookupApiKey(Properties props) {
          String apiKey = null;
          // lookup from system property td.logger.api.key. If it exists, writes/updates td.api.key.
          if (props.containsKey(Config.TD_LOGGER_API_KEY)) {
              apiKey = props.getProperty(Config.TD_LOGGER_API_KEY);
              props.setProperty(Config.TD_API_KEY, apiKey);
          }
          return apiKey;
      }
docs: Define order for API key lookup.
  1. lookup props's 'td.logger.api.key'