docs: public void map(K key,
                      V value,
                      OutputCollector<BytesWritable, BytesWritable> output,
                      Reporter reporter) throws IOException {
  
          byte[] keyBytes = keySerializer.toBytes(makeKey(key, value));
          byte[] valBytes = valueSerializer.toBytes(makeValue(key, value));
  
          this.collectorWrapper.setCollector(output);
          this.mapper.map(keyBytes, valBytes, this.collectorWrapper);
      }