code: private static void getIndexReaders(List<IndexReader> readers, IndexReader reader)
     {
        if (reader instanceof MultiIndexReader)
        {
           for (IndexReader r : ((MultiIndexReader)reader).getIndexReaders())
           {
              getIndexReaders(readers, r);
           }
        }
        else
        {
           readers.add(reader);
        }
     }
docs: Checks if <code>reader</code> is of type {@link MultiIndexReader} and if
  so calls itself recursively for each reader within the
  <code>MultiIndexReader</code> or otherwise adds the reader to the list.
  
  @param readers  list of index readers.
  @param reader   reader to decompose