code: public static void encodeDesc(Double value, byte[] dst, int dstOffset) {
          if (value == null) {
              DataEncoder.encode(~0x7fffffffffffffffL, dst, dstOffset);
          } else {
              encodeDesc(value.doubleValue(), dst, dstOffset);
          }
      }
docs: Encodes the given Double object into exactly 8 bytes for descending
  order. A non-canonical NaN value is used to represent null.
  
  @param value optional Double value to encode
  @param dst destination for encoded bytes
  @param dstOffset offset into destination array