code: public BigInteger asBigInteger() throws IOException {
          if (_value instanceof BigInteger) {
              return (BigInteger) _value;
          }
          if (_value instanceof BigDecimal) {
              BigDecimal dec = (BigDecimal) _value;
              return dec.toBigInteger();
          }
          return BigInteger.valueOf(_value.longValue());
      }
docs: /*
  ********************************************************************
  /* Extended API
  ********************************************************************