public void set(Timestamp t) {
    if (t == null) {
      timestamp.set(null);
      return;
    }
    timestamp.set(t);
    bytesEmpty = true;
    timestampEmpty = false;
  }
true if data is stored in timestamp field rather than byte arrays.
     allows for lazy conversion to bytes when necessary
false otherwise
serde/src/java/org/apache/hadoop/hive/serde2/io/TimestampWritableV2.java