output: #fixed code
                                  @Override
      public int scan(String table, String startkey, int recordcount,
              Set<String> fields, Vector<HashMap<String, ByteIterator>> result) {
          MongoCursor<Document> cursor = null;
          try {
              MongoCollection<Document> collection = database
                      .getCollection(table);
  
              Document scanRange = new Document("$gte", startkey);
              Document query = new Document("_id", scanRange);
              Document sort = new Document("_id", INCLUDE);
              Document projection = null;
              if (fields != null) {
                  projection = new Document();
                  for (String fieldName : fields) {
                      projection.put(fieldName, INCLUDE);
                  }
              }
  
              cursor = collection.find(query)
                      .projection(projection).sort(sort).limit(recordcount).iterator();
              if (!cursor.hasNext()) {
                  System.err.println("Nothing found in scan for key " + startkey);
                  return 1;
              }
              while (cursor.hasNext()) {
                  HashMap<String, ByteIterator> resultMap = new HashMap<String, ByteIterator>();
  
                  Document obj = cursor.next();
                  fillMap(resultMap, obj);
  
                  result.add(resultMap);
              }
  
              return 0;
          }
          catch (Exception e) {
              System.err.println(e.toString());
              return 1;
          }
          finally {
              if (cursor != null) {
                  cursor.close();
              }
          }
      }
input: #vulnerable code 
                                  @Override
      public int scan(String table, String startkey, int recordcount,
              Set<String> fields, Vector<HashMap<String, ByteIterator>> result) {
          MongoCursor<Document> cursor = null;
          try {
              MongoCollection<Document> collection = database
                      .getCollection(table);
  
              Document scanRange = new Document("$gte", startkey);
              Document query = new Document("_id", scanRange);
              Document sort = new Document("_id", INCLUDE);
              Document projection = null;
              if (fields != null) {
                  projection = new Document();
                  for (String fieldName : fields) {
                      projection.put(fieldName, INCLUDE);
                  }
              }
  
              cursor = collection.withReadPreference(readPreference).find(query)
                      .projection(projection).sort(sort).limit(recordcount).iterator();
              if (!cursor.hasNext()) {
                  System.err.println("Nothing found in scan for key " + startkey);
                  return 1;
              }
              while (cursor.hasNext()) {
                  HashMap<String, ByteIterator> resultMap = new HashMap<String, ByteIterator>();
  
                  Document obj = cursor.next();
                  fillMap(resultMap, obj);
  
                  result.add(resultMap);
              }
  
              return 0;
          }
          catch (Exception e) {
              System.err.println(e.toString());
              return 1;
          }
          finally {
              if (cursor != null) {
                  cursor.close();
              }
          }
      } 
                              #location 20 
                              #vulnerability type THREAD_SAFETY_VIOLATION