public static String unsupportedVersionMessage(final short ordinal) {
    return String.format(
        "Peer or client version with ordinal %s not supported. Highest known version is %s",
        ordinal, CURRENT.name);
  }
an invalid KnownVersion used for tests and instead of null values
geode-serialization/src/main/java/org/apache/geode/internal/serialization/KnownVersion.java