@Override
  public void transientInit(Configuration conf) throws HiveException {
    super.transientInit(conf);
    if (formatter == null) {
      formatter = InstantFormatter.ofConfiguration(conf);
    }
  }
Return Unix Timestamp.
Extends {@link VectorUDFTimestampFieldString}
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/VectorUDFUnixTimeStampString.java