@Override
  public byte[] toByteArray() {
    ComparatorProtos.NullComparator.Builder builder = ComparatorProtos.NullComparator.newBuilder();
    return builder.build().toByteArray();
  }
Returns The comparator serialized using pb
hbase-client/src/main/java/org/apache/hadoop/hbase/filter/NullComparator.java