修改原始碼如下：

    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
        while(true){
            if (currentDoc >= numDocs) {
                return false;
            }
            SolrDocument doc = solrDocs.get(currentDoc);
            String digest = (String) doc.getFieldValue(SolrConstants.DIGEST_FIELD);
            if
 
(digest == null || digest.isEmpty()){
                currentDoc++;
                continue;
            }
            text.set(digest);
            record.readSolrDocument(doc);
            currentDoc++;
            break;
        }
      return true;
    }