code: @Override
    public final FieldsConsumer fieldsConsumer(SegmentWriteState state)
        throws IOException {
      if (delegatePostingsFormat != null) {
        return new MtasFieldsConsumer(
            delegatePostingsFormat.fieldsConsumer(state), state, getName(),
            delegatePostingsFormat.getName());
      } else {
        PostingsFormat pf = Codec.forName(delegateCodecName).postingsFormat();
        return pf.fieldsConsumer(state);
      }
    }
docs: /*
  (non-Javadoc)
  
  @see
  org.apache.lucene.codecs.PostingsFormat#fieldsConsumer(org.apache.lucene
  .index.SegmentWriteState)