code: public DecoratedKey partitionKey(Document document) {
          String string = document.get(FIELD_NAME);
          ByteBuffer partitionKey = ByteBufferUtils.fromString(string);
          return partitionKey(partitionKey);
      }
docs: Returns the {@link DecoratedKey} contained in the specified Lucene {@link Document}.
  
  @param document the {@link Document} containing the partition key to be get.
  @return The {@link DecoratedKey} contained in the specified Lucene {@link Document}.