Collection<String> readHostedLocators() {
    if (optionalFields == null || optionalFields.isEmpty()) {
      return null;
    }
    Collection<String> hostedLocators = null;
    String hostedLocatorsString = optionalFields.getProperty(HOSTED_LOCATORS);
    if (hostedLocatorsString != null && !hostedLocatorsString.isEmpty()) {
      StringTokenizer st = new StringTokenizer(hostedLocatorsString, COMMA_DELIMITER);
      hostedLocators = new ArrayList<>();
      while (st.hasMoreTokens()) {
        String locatorString = st.nextToken();
        if (locatorString != null && !locatorString.isEmpty()) {
          hostedLocators.add(locatorString);
        }
      }
      if (hostedLocators.isEmpty()) {
        hostedLocators = null;
      }
    }
    return hostedLocators;
  }
Check for the optional field {@link #HOSTED_LOCATORS} and return the value or null.
geode-core/src/main/java/org/apache/geode/distributed/internal/StartupMessageData.java