code: protected Document doGet(String spaceId, String key) throws IOException {
          Term termGet = buildIdTerm(spaceId, key);
          IndexSearcher indexSearcher = getIndexSearcher();
          TopDocs result = indexSearcher.search(new TermQuery(termGet), 1);
          ScoreDoc[] hits = result != null ? result.scoreDocs : null;
          Document doc = hits != null && hits.length > 0 ? indexSearcher.doc(hits[0].doc) : null;
          return doc;
      }
docs: Fetch a document, identified by {@code spaceId:key}, from index.
  
  @param spaceId
  @param key
  @return
  @throws IOException