Review

class SegmentMerger {
  private void mergeNorms() throws IOException {
    byte[] normBuffer = null;
    IndexOutput output = null;
    try {
      int numFieldInfos = fieldInfos.size();
      for (int i = 0; i < numFieldInfos; i++) {
        FieldInfo fi = fieldInfos.fieldInfo(i);
        if (fi.isIndexed && !fi.omitNorms) {
          if (output == null) { 
            output = directory.createOutput(segment + "." + IndexFileNames.NORMS_EXTENSION);
            output.writeBytes(NORMS_HEADER,NORMS_HEADER.length);
          }
          for (Iterator iter = readers.iterator(); iter.hasNext();) {
            IndexReader reader = (IndexReader) iter.next();
            int maxDoc = reader.maxDoc();
            if (normBuffer == null || normBuffer.length < maxDoc) {
              // the buffer is too small for the current segment
              normBuffer = new byte[maxDoc];
            }
            reader.norms(fi.name, normBuffer, 0);
            if (!reader.hasDeletions()) {
              //optimized case for segments without deleted docs
              output.writeBytes(normBuffer, maxDoc);
            } else {
              // this segment has deleted docs, so we have to
              // check for every doc if it is deleted or not
              for (int k = 0; k < maxDoc; k++) {
                if (!reader.isDeleted(k)) {
                  output.writeByte(normBuffer[k]);
                }
              }
            }
            checkAbort.work(maxDoc);
          }
        }
      }
    } finally {
      if (output != null) { 
        output.close();
      }
    }
  }

}