@Override
  public int compareTo(Object o) {
    // A Null token is equal to other Null token and less than any other object
    // except UNDEFINED
    if (o.equals(this)) {
      return 0;
    } else if (o.equals(QueryService.UNDEFINED)) {
      return 1;
    } else {
      return -1;
    }
  }
A Token representing null.

@since GemFire cedar
geode-core/src/main/java/org/apache/geode/cache/query/internal/NullToken.java