@Override
  public boolean isEmpty() {
    return delColMap.size() == 1 && delColMap.get(Long.MAX_VALUE).mvccCountingMap.size() == 1
      && delFamMap.size() == 1 && delFamMap.get(Long.MAX_VALUE).mvccCountingMap.size() == 1;
  }
This method is not idempotent, we will save some info to judge VERSION_MASKED.
@param cell - current cell to check if deleted by a previously seen delete
@return We don't distinguish DeleteColumn and DeleteFamily. We only return code for column.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/querymatcher/NewVersionBehaviorTracker.java