@HiveDecimalVersionV1
  public HiveDecimal multiply(HiveDecimal dec) {
    HiveDecimal result = new HiveDecimal();
    if (!fastMultiply(
        dec,
        result)) {
      return null;
    }
    return result;
  }
Multiply two decimals.
<p>
NOTE: Overflow Determination for Multiply
<p>
  OldDecimal.multiply performs the multiply with BigDecimal but DOES NOT ALLOW ROUNDING
  (i.e. no throwing away lower fractional digits).
<p>
  CONSIDER: Allowing rounding.  This would eliminate cases today where we return null for
            the multiplication result.
<p>
IMPLEMENTATION NOTE: HiveDecimalV1 code does this:
<p>
return create(bd.multiply(dec.bd), false);
storage-api/src/java/org/apache/hadoop/hive/common/type/HiveDecimal.java