code: public void error(long requestId, String message, Object... args) {
          if (requestId != RequestTag.NON_EXISTENT_ID) {
              log.error(String.format("[requestId=%d] %s", requestId, message), args);
          } else {
              log.error(message, args);
          }
      }
docs: Writes an error-level log line on the provided logger consisting of a header tag (e.g., requestId) and the message
  passed (plus the arguments) in the case that the request id comes from a client request (i.e., not a default one).
  Note that the message may include formatting anchors to be filled by subsequent arguments.
  
  @param requestId     Tag used as header for the log line.
  @param message       Message to log including formatting anchors.
  @param args          Additional arguments to log expected to fill in the message's formatting anchors.