@HiveDecimalWritableVersionV1
  public void set(HiveDecimal value) {
    if (value == null) {
      fastReset();
      isSet = false;
    } else {
      fastSet(value);
      isSet = true;
    }
  }
Set the writable's current value to a HiveDecimal's value.
<p>
Afterwards, the isSet() method will return true, unless value is null.
storage-api/src/java/org/apache/hadoop/hive/serde2/io/HiveDecimalWritable.java