TupleProtocol#writeBitSet unintentionally writes a variable length byte array

BitSet.length() only returns the highest-set-bit, meaning that if you have more than 8 optional fields, and the 9+th optional field is unset, then only the first byte's worth of bits will be serialized. This leads to a problem on the read side, where the bit vector is assumed to be fixed width, and arbitrary deserialization occurs.