code: private void addKeyToTuple(Tuple tuple, ByteBuffer key, CfDef cfDef, AbstractType comparator) throws IOException
      {
          if( comparator instanceof AbstractCompositeType )
          {
              setTupleValue(tuple, 0, composeComposite((AbstractCompositeType)comparator,key));
          }
          else
          {
              setTupleValue(tuple, 0, cassandraToObj(getDefaultMarshallers(cfDef).get(MarshallerType.KEY_VALIDATOR), key));
          }
  
      }
docs: add key to a tuple