code: public ArrayList<Entry<Text, Text>> generateKeyValPairs(Object key,
                                                            Object val) {
      ArrayList<Entry<Text, Text>> retv = new ArrayList<Entry<Text, Text>>();
      if (this.theAggregatorDescriptor != null) {
        retv = this.theAggregatorDescriptor.generateKeyValPairs(key, val);
      }
      return retv;
    }
docs: Generate a list of aggregation-id/value pairs for the given key/value pairs
  by delegating the invocation to the real object.
  
  @param key
  input key
  @param val
  input value
  @return a list of aggregation id/value pairs. An aggregation id encodes an
  aggregation type which is used to guide the way to aggregate the
  value in the reduce/combiner phrase of an Aggregate based job.