@Override
    public Object convert(Object obj) {
      throw new UnsupportedOperationException("Use extractAndConvert for ListConvertor");
    }
Convert the given writable to a message.
@param writable The writable object containing the message.
@return The converted message object.
@throws SerDeException
ql/src/java/org/apache/hadoop/hive/ql/io/protobuf/ProtobufSerDe.java