code: @Nullable
    public Date timestamp() {
      // It's unclear if this will ever be null. So we're being safe.
      String timestamp = getString(TIMESTAMP_KEY);
      if (isNullOrEmpty(timestamp)) {
        return null;
      }
      return parseISO8601Date(timestamp);
    }
docs: Set a timestamp the event occurred.
  
  <p>This library will automatically create and attach a timestamp to all events.
  
  @see <a href="https://segment.com/docs/spec/common/#timestamps">Timestamp</a>