code: @Override
    public QueryBasedHiveConversionEntity readRecord(QueryBasedHiveConversionEntity reuse) throws DataRecordException, IOException {
  
      if (this.conversionEntities.isEmpty()) {
        return null;
      }
  
      return this.conversionEntities.remove(0);
    }
docs: There is only one record ({@link QueryBasedHiveConversionEntity}) to be read. This {@link QueryBasedHiveConversionEntity} is
  removed from {@link #conversionEntities} list after it is read. So when gobblin runtime calls this method the second time, it returns a null