public ConflationKey getConflationKey() {
    return null; // by default conflate nothing; override in subclasses
  }
@return null if message is not conflatable. Otherwise return a key that can be used to identify
        the entry to conflate.
@since GemFire 4.2.2
geode-core/src/main/java/org/apache/geode/distributed/internal/DistributionMessage.java