private void checkBytes() {
    if (bytesEmpty) {
      // Populate byte[] from Timestamp
      convertTimestampToBytes(timestamp, internalBytes, 0);
      offset = 0;
      currentBytes = internalBytes;
      bytesEmpty = false;
    }
  }
The data of TimestampWritable can be stored either in a byte[]
or in a Timestamp object. Calling this method ensures that the byte[]
is populated from the Timestamp object if previously empty.
serde/src/java/org/apache/hadoop/hive/serde2/io/TimestampWritable.java