code: public void addFields(Document document, DecoratedKey partitionKey) {
          String serializedKey = ByteBufferUtils.toString(partitionKey.getKey());
          Field field = new StringField(FIELD_NAME, serializedKey, Store.YES);
          document.add(field);
      }
docs: Adds to the specified {@link Document} the {@link Field}s associated to the specified raw partition key.
  
  @param document     The document in which the fields are going to be added.
  @param partitionKey The raw partition key to be converted.