@Override
  public BigDecimal add(BigDecimal bd1, BigDecimal bd2) {
    if (bd1 == null ^ bd2 == null) {
      return (bd1 == null) ? bd2 : bd1; // either of one is null.
    }
    if (bd1 == null) {
      return null;
    }
    return bd1.add(bd2);
  }
ColumnInterpreter for doing Aggregation's with BigDecimal columns. This class is required at the
RegionServer also.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/coprocessor/BigDecimalColumnInterpreter.java